EXPERIMENTAL  STUDIES 

IN 

ELECTRICITY  AND  MAGNETISM 


N  1  P  H  E  R 


Experimental  Studies 

IN 

Electricity  and  Magnetism 


BY 

FRANCIS  E.  NIPHER 


WITH  9  PLATES,  29  TEXT  FIGURES 


PHILADELPHIA 
P.   BLAKISTON'S   SON   &   CO. 

1012  WALNUT   STREET 


COPYRIGHT,  IQM,  BY  FRANCIS  E  NIPHER 


THE.MAPLE«PRES8-TORK.PA 

' 


INTRODUCTION 

The  published  papers  of  Professor  Nipher  bearing  upon  the 
nature  of  the  electric  discharge  contain  much  evidence  upon 
views  which  have  long  been  under  consideration.  This  evidence 
was  necessarily  more  or  less  fragmentary  in  character,  as  it 
appeared  in  successive  papers  in  the  Transactions  of  a  learned 
society.  While  calling  upon  him  recently  in  his  laboratory,  I 
advised  him  to  present  his  work  to  the  public  in  book  form.  I 
consider  it  of  importance  that  it  should  receive  attention  from 
scientific  men,  and  it  will  certainly  be  of  interest  to  the  general 
reader. 

THOMAS  R.  LYLE,  F.  R.  S. 

THE  UNIVERSITY,  MELBOURNE,  AUSTRALIA. 


-OR  THE  ONE- 
ERRATA  .CTRICITY 

Page    17,  line   10  from   bottom,    for    "cemf** 

read  '  'came. ' '  tO  prepare  a  papfr  f °r 

CA   ..      „  ,                 .       ((                               >  of  Arts  and  Science. 

rage  3U,  line  3  trom  top,  for      service     read           *  . 

«  ,    .    ,,  )ject  assigned  by  the 

-0    »  ..  D,  was  "Present  Prob- 

rage  73,  first  column,  line   17  from  bottom,  .  ,  ... 

f      «  ,,        .  «  ,,  le  problems  which  was 

tor     steamers     read     streamers. 

arge.     A  consideration 

strongly  favor  the  one- 
man  ineory.  since  uiai  Lime  neariy  an  of  my  time  has  been 
devoted  to  a  search  for  additional  evidence  of  an  experimental 
character  which  would  be  readily  explainable  by  one  of  these  theo- 
ries and  not  by  the  other.  Most  of  this  work  has  been  published 
by  the  Academy  of  Science  of  St.  Louis.1  Recently  several  friends 
have  strongly  advised  that  this  evidence  should  be  presented  to 
the  public  in  a  more  logically  connected  form  than  was  possible 
in  the  original  papers.  This  little  volume  is  a  response  to  such 
requests. 

When  a  metal  sphere,  suspended  on  a  silk  thread,  is  placed 
between  the  discharge  knobs  of  an  electrical  machine,  it  oscillates 
to  and  fro  between  the  knobs.  It  is  alternately  attracted  by  and 
then  repelled  from  each  terminal. 

Assume  now  that  the  space  between  the  knobs  is  occupied  only 
by  air  under  atmospheric  conditions.  Each  molecule  of  air  is 
then  seeking  to  behave  as  did  that  metal  sphere.  It  is  manifestly 
impossible  for  any  one  of  them  to  do  this.  A  stream  of  molecules 
is  repelled  from  each  terminal  toward  the  opposite  one.  They 
mingle  with  each  other.  Electrically  these  opposing  streams  are 
friendly,  but  mechanically  they  are  in  pronounced  opposition  to 
each  other. 

1  Trans.  Vol.    XIX,  No.  i,  pp.  1-20,  with  10  Plates,  1910. 
Vol.    XIX,  No.  4,  pp.  57-72,  with  8  Plates,  1910. 
Vol.      XX,  No.  i,  pp.  1-16,  with  6  Plates,  1911. 
Vol.    XXI,  No.  3,  pp.  79-87,  with  i  Plate,  1912. 
Vol.  XXII,  No.  2,  pp.  59-65,  with  2  Plates,  1913. 
Vol.  XXII,  No.  4,  pp.  109-124,  with  4  Plates,  1913. 


EXPERIMENTAL  EVIDENCE  FOR  THE  ONE- 
FLUID  THEORY  OF  ELECTRICITY 

In  the  summer  of  1903  I  was  requested  to  prepare  a  paper  for 
presentation  to  the  International  Congress  of  Arts  and  Science, 
held  in  St.  Louis  during  1904.  The  subject  assigned  by  the 
President  of  the  Congress,  Simon  Newcomb,  was  "Present  Prob- 
lems in  the  Physics  of  Matter. "  One  of  the  problems  which  was 
considered  was  the  nature  of  electrical  discharge.  A  consideration 
of  phenomena  then  well  known  seemed  to  strongly  favor  the  one- 
fluid  theory.  Since  that  time  nearly  all  of  my  time  has  been 
devoted  to  a  search  for  additional  evidence  of  an  experimental 
character  which  would  be  readily  explainable  by  one  of  these  theo- 
ries and  not  by  the  other.  Most  of  this  work  has  been  published 
by  the  Academy  of  Science  of  St.  Louis.1  Recently  several  friends 
have  strongly  advised  that  this  evidence  should  be  presented  to 
the  public  in  a  more  logically  connected  form  than  was  possible 
in  the  original  papers.  This  little  volume  is  a  response  to  such 
requests. 

When  a  metal  sphere,  suspended  on  a  silk  thread,  is  placed 
between  the  discharge  knobs  of  an  electrical  machine,  it  oscillates 
to  and  fro  between  the  knobs.  It  is  alternately  attracted  by  and 
then  repelled  from  each  terminal. 

Assume  now  that  the  space  between  the  knobs  is  occupied  only 
by  air  under  atmospheric  conditions.  Each  molecule  of  air  is 
then  seeking  to  behave  as  did  that  metal  sphere.  It  is  manifestly 
impossible  for  any  one  of  them  to  do  this.  A  stream  of  molecules 
is  repelled  from  each  terminal  toward  the  opposite  one.  They 
mingle  with  each  other.  Electrically  these  opposing  streams  are 
friendly,  but  mechanically  they  are  in  pronounced  opposition  to 
each  other. 

1  Trans.  Vol.    XIX,  No.  i,  pp.  1-20,  with  10  Plates,  1910. 
Vol.    XIX,  No.  4,  pp.  57-72,  with  8  Plates,  1910. 
Vol.      XX,  No.  i,  pp.  1-16,  with  6  Plates,  1911. 
Vol.    XXI,  No.  3,  pp.  79-87,  with  i  Plate,  1912. 
Vol.  XXII,  No.  2,  pp.  59-65,  with  2  Plates,  1913. 
Vol.  XXII,  No.  4,  pp.  109-124,  with  4  Plates,  1913. 


2  The  Metal  Shield 

The  machine  used  for  this  work  was  a  large  four-plate  influence 
machine.  The  arrangement  best  adapted  to  produce  the  results 
to  be  described  is  shown  in  Fig.  i.  The  machine  terminals  are 
each  connected  with  external  knobs  A  and  A1,  between  which  are 
smaller  discharge  terminals,  having  smaller  knobs  at  each  end. 
These  discharge  rods  are  movable.  Small  spark  gaps  may  thus 
be  made  at  a  and  a1. 

For  the  work  to  be  first  described,  the  condensers  were  removed. 
A  sheet  of  copper  CC  mounted  on  insulating  supports  was  placed 
midway  between  the  discharge  terminals.  Between  the  positive 
terminal  and  the  copper  plate  a  large  diverging  brush  discharge 
appears.  Its  form  depends  somewhat  upon  the  length  of  the 
minute  gaps  at  a  and  a1.  It  extends  over  an  area  5  or  6  cm. 


in  diameter  upon  the  copper  plate.     The  distance  between  the 
plate  and  the  positive  terminal  was  about  6  or  7  cm. 

The  small  knob  forming  the  negative  terminal  was  covered 
with  the  negative  glow,  but  between  this  glow  and  the  copper 
plate  the  space  was  absolutely  dark.  It  was,  however,  evident 
that  there  was  an  active  discharge  across  this  dark  space  if  there 
was  a  small  gap  at  either  a  or  a1. 

A  small  windmill  having  vanes  of  thin  mica  mounted  in  a  hub 
of  hard  rubber,  and  turning  on  pivots  of  vulcanized  fiber  will 
revolve  when  placed  in  either  gap.  In  the  positive  column,  the 


Effect  of  the  Metal  Shield  3 

air  is  thus  shown  to  be  moving  toward  the  plate,  and  from  the 
positive  terminal.  In  the  dark  space  the  air  is  moving  in  the 
opposite  direction.  In  the  positive  column  the  rotation  was  about 
like  that  which  could  be  produced  by  walking  with  the  wind- 


FlG.    2. 


mill  in  still  air  with  a  velocity  of  1.5  m.  per  second.     In  the 
dark  space  the  speed  was  somewhat  less. 

If  the  copper  plate  is  moved  toward  the  negative  terminal, 
the  luminous  column  on  the  positive  side  becomes  longer.  It  still 
terminates  on  the  plate.  If  it  is  moved  in  the  opposite  direction, 


FIG.  3. 


the  dark  space  becomes  longer.     It  follows  the  plate  up  to  the 
positive  terminal. 

A  camera  photograph  of  the  negative  glow  and  the  luminous 
positive  column  is  presented  in  Fig.  2.  A  large  copying  camera 
was  used.  An  exposure  of  15  minutes  was  made  in  a  dark  room. 


4  Oscillations 

The  metal  plate  CC  of  Fig.  i  was  removed.  A  minute  spark- 
gap  was  made  at  a1.  The  contact  at  a  was  made  as  complete  as 
possible,  so  that  no  luminous  point  is  seen  at  this  contact.  The 
discharge  then  swept  through  the  entire  spark-gap  of  about  15  cm. 
The  photograph  of  this  luminous  column  as  taken  by  the  camera 


FIG   4. 

is  shown  in  Fig.  3.  The  exposure  was  about  5  minutes.  The 
mica  windmill  shows  a  feeble  wind  from  the  positive  terminal. 
If  the  gap  at  a1  is  made  somewhat  larger,  the  discharge  is  then 
filled  throughout  with  small  disruptive  sparks,  and  the  windmill 
will  not  operate.  If  the  gap  a1  is  made  still  longer  appearing,  as 


FIG.  5. 

seen  in  Fig.  4,  a  strong  positive  wind  causes  the  windmill  to  rotate 
so  rapidly  that  its  vanes  are  invisible.1  This  wind  sweeps  through 
the  entire  gap.  The  discharge  is  not  then  disruptive  in  character. 

1  Fig.  4  is  from  a  photograph  of  this  gap,  a*,  but  the  outlines  of  the  knobs  were 
only  faintly  visible.     They  are  drawn  in  ink. 


The  Canal  Ray  5 

If  the  gap  at  a1  is  closed  and  that  at  a  is  opened,  the  luminous 
streamers  forming  the  positive  column  are  beaten  back  by  a  blast 
of  air  from  the  negative  terminal.  The  mica  windmill  shows  that 
the  negative  wind  now  sweeps  the  entire  gap.  Fig.  5  is  a  camera 
photograph  of  the  discharge.  The  slightest  change  in  the  length 
of  the  spark-gaps  a  and  a1  produces  marked  changes  in  the  form 
and  character  of  the  discharge  through  the  long  gap.  Such 
changes  are  attended  by  variation  in  the  pitch  of  musical  tones 
which  accompany  the  discharge.  When  both  of  the  gaps  a  and  a1 
are  closed  the  negative  glow  is  still  visible,  but  the  luminous 
column  is  only  very  faintly  visible. 

The  copper  plate  CC  of  Fig.   i  was  again  placed  in  position 


FIG.  6. 

as  in  the  discharge  shown  in  Fig.  2.     A  hole  having  a  diameter 
of  about  5  mm.  was  made  in  the  copper  plate. 

The  positive  column  on  the  positive  side  of  the  plate  was 
not  appreciably  changed  in  form  by  the  presence  of  this  hole, 
but  it  then  extended  through  the  hole  to  the  negative  glow, 
as  seen  in  the  two  Figs.  6  and  6a.  The  relative  luminosity  of 
the  canal  ray  passing  through  this  hole,  and  of  the  positive  column 
of  which  it  is  a  prolongation,  depends  upon  the  lengths  of  the 
oscillation  gaps  a  and  a1.  In  these  gaps  there  is  a  continuous 
surging  to  and  fro  of  air  molecules.  It  is  evidently  a  time  alterna- 
tion of  convection  and  conduction  discharge.  In  the  one  case 
the  negative  corpuscles  are  carried  across  the  gap  by  super-charged 


6  The  Dark  Discharge 

molecules.  This  is  a  dark  discharge.  When  these  molecules 
return  they  have  lost  not  only  the  excess  but  a  part  of  their  own 
normal  charges.  They  then  form  a  conductor,  through  which  a 

FT :---:•--;--;•-;<- -        -     -  n 


FIG.  6a. 


luminous  transfer  by  conduction  takes  place.  These  vibrations 
show  their  presence  by  musical  tones  of  high  pitch.  The  pitch 
of  these  notes  rises  as  the  gaps  a  and  a1  are  made  shorter.  The 
sounds  cease  when  these  gaps  are  closed.  In  Fig.  6a,  a  minute 


FIG.  7. 

gap  of  less  than  a  mm.  existed  in  the  negative  approach  line  at  a1. 
In  Fig.  6  this  gap  was  closed  and  a  similar  gap  was  made  at  a 
in  the  positive  line.  In  Fig.  7  both  gaps  were  closed.  In  each 


Drainage  Channels  7 

case  a  flash  light  was  used  at  the  end  of  a  5 -minute  exposure, 
in  order  to  secure  an  image  of  the  knobs.  The  diameter  of  the 
knobs  was  1.8  cm. 

When  both  gaps  a  and  a1  are  closed  and  the  lines  leading  from 
the  machine  terminals  to  the  main  gap  are  metallic  throughout, 
as  in  Fig.  7,  an  active  negative  glow  exists  in  front  of  the  negative 
knob.  The  mica  windmill  shows  that  the  air  is  being  urged  across 
the  negative  dark  space  to  the  copper  plate.  In  the  gap  between 
the  copper  plate  and  the  positive  knob,  there  were  no  luminous 
streamers,  but  they  formed  when  the  windmill  was  placed  in  this 
gap,  and  a  faint  motion  of  the  air  toward  the  copper  plate  was  then 
indicated. 


FIG.  8. 


The  front  edge  of  the  plate  is  not  in  focus,  and  its  image  is 
rather  imperfectly  reproduced  in  the  original,  and  does  not  appear 
in  Fig.  7. 

In  Fig.  7  a  strongly  marked  glow  is  shown  on  the  surface  of  the 
positive  knob.  It  covers  the  hemisphere  which  faces  the  copper 
plate.  This  glow  differs  from  the  negative  glow  at  the  other  knob. 
It  gives  the  front  of  the  knob  the  appearance  of  being  at  a  red 
heat.  Scintillations  are  occasionally  visible  over  this  luminous 
surface.  They  are  perhaps  the  beginnings  of  drainage  streamers. 
It  seems  evident  that  air  molecules  in  contact  with  this  luminous 
part  of  the  knob  are  delivering  corpuscles  to  the  knob,  but  the 
drainage  luminescence  does  not  extend  beyond  the  layer  in  close 


8  Drainage  Channels 

contact  with  the  knob.  If  the  contacts  at  either  a  or  a1  are  dis- 
turbed so  that  any  luminous  effects  exist  at  these  gaps,  this  positive 
glow  partly  or  wholly  disappears  and  one  or  more  luminous  stream- 
ers shoot  out  from  the  positive  knob.  The  drainage  inflow  to  the 
positive  terminal  is  then  through  and  along  these  conducting 
channels.  If  the  gap  at  a  in  the  positive  line  is  slightly  increased 
in  length,  the  luminous  streamers  appear  in  arc-like  forms  from 
points  around  the  central  line  of  discharge.  These  streamers  are 
continually  vibrating  as  in  the  case  when  convection  and  conduc- 
tion winds  in  opposite  directions  exist  side  by  side. 

In  Fig.  8  the  discharge  knobs  were  displaced  laterally.     The 
hole  in  the  copper  plate  was  opposite  the  positive  knob,  and  in 


FIG.  9. 

the  central  part  of  the  cone-shaped  positive  column.  It  will 
be  observed  that  the  canal  ray  passing  through  this  hole  turns 
toward  and  extends  to  the  negative  glow.  A  flash  light  fol- 
lowed this  exposure.  In  Fig.  9  the  conditions  were  precisely 
similar,  except  that  the  hole  in  the  copper  sheet  was  opposite 
the  negative  terminal.  The  luminous  cone  has  the  same  form  as 
before.  It  will  be  observed  that  the  discharge  from  the  nega- 
tive knob  across  the  dark  space  to  the  hole  in  the  copper  plate, 
has  an  influence  upon  the  drainage  to  the  positive  terminal. 
A  secondary  positive  column  forms  at  the  lowest  point  on  the  posi- 
tive knob,  and  curves  toward  the  hole  in  the  copper  plate. 

In  Fig.  10  the  discharge  terminals  are  in  line  with  each  other 


Shadow  Effects  9 

but  the  copper  plate  was  displaced.  The  canal  ray  was  partly 
obstructed  by  a  small  disc  of  copper,  mounted  upon  the  end  of  a 
glass  tube. 

Fig.  ii  shows  the  shadow  in  the  positive  column  made  by  a 


FIG.  10.  ] 

glass  tube  placed  midway  between  the  positive  knob,  and  the  cop- 
per plate.  The  end  of  the  tube  faces  the  camera.  There  was  no 
hole  in  the  copper  plate.  It  will  be  observed  that  the  shape 
of  the  shadow  is  somewhat  modified  by  the  air  current  which 
drifted  around  the  obstruction. 


FIG.  n. 


A  couple  of  two-gallon  Leyden  jars  were  then  connected 
with  the  machine  terminals  and  the  experiments  shown  in  Figs.  8 
and  9  were  repeated.  Five  loud  disruptive  discharges  are  shown 
in  Fig.  12.  On  the  negative  side  of  the  copper  plate  these  dis- 


IO 


Park  of  Disruptive  Discharge 


charges  with  one  exception  followed  along  the  line  of  the  canal 
ray  shown  in  Fig.  8.  They  passed  through  the  hole  in  the  copper 
plate. 


FIG.  12. 


In  Fig.  13  the  conditions  were  only  changed  by  hanging  a 
thin  strip  of  paper  over  the  top  of  the  copper  plate.  This  paper 
covered  the  hole,  and  prevented  the  passage  of  the  canal  ray. 

In  Fig.  14,  the  conditions  of  Fig.  9  were  reproduced.     The 


FIG.  13. 

hole  was  open,  but  it  was  opposite  the  negative  discharge  knob. 
The  discharge  rods  were  then  placed  in  line  with  each  other,  as  in 
Fig.  2.  The  distance  between  the  knobs  was  about  13  cm.  The 


Conditions  for  Disruptive  Discharge  n 

Leyden  jars  were  still  attached  to  the  machine  terminals.  The 
copper  plate,  having  no  opening  in  it  was  hung  between  the  spark 
knobs  on  long  silk  threads.  The  plate  moved  into  a  position  of 
stable  equilibrium  at  a  distance  of  3  or  4  cm.  from  the  negative 
knob.  In  this  position  loud  spark  discharges  passed  through  the 
plate  as  readily  as  they  would  pass  when  it  was  removed.  The 
dark  space  still  existed  between  the  plate  and  the  negative  glow. 
Moving  the  plate  farther  from  the  negative  terminal,  the  dis- 
charges ceased.  A  position  could  be  found  where  a  change  of  a 
fraction  of  a  mm.  in  the  position  of  the  metal  plate  would  produce 
a  radical  change  in  the  discharge.  In  one  position  a  torrent  of  loud 
sparks  passes.  In  the  other  position  disruptive  discharge  ceases. 
When  the  conditions  as  described  in  connection  with  Fig.  4 


FIG.  14. 

are  imposed,  the  same  results  may  be  secured  by  placing  the  metal 
plate  in  the  smaller  gap  a1. 

When  the  main  spark  gap  is  made  long  enough  so  that  sparks 
will  still  pass  between  the  knobs,  but  the  limit  is  being  approached, 
the  interposition  of  a  copper  plate  of  sufficient  size  will  cut  off 
the  drainage  column  as  has  been  shown  in  previous  figures.  It  then 
appears  at  the  edges  and  corners  of  the  interposed  plate.  In  Fig. 
15  these  conditions  are  shown.  The  luminous  column  curved  to- 
ward the  negative  knob  from  the  edge  of  the  plate.  Just  before 
the  spark  passed  it  had  nearly  reached  the  negative  glow.  The 
disruptive  discharge  then  passed  along  this  drainage  channel  from 


12  Conditions  for  Disruptive  Discharge 

the  edge  of  the  insulated  copper  plate  to  the  negative  knob.  The 
plate  was  near  enough  to  the  positive  terminal,  so  that  it  might  be 
considered  a  part  of  that  terminal.  The  disruptive  discharge  does 
not  follow  the  line  of  least  distance.  It  follows  the  line  of  least 
resistance.  The  conditions  are  similar  to  those  represented  in 
Fig.  12.  If  the  exposure  had  ceased  just  before  the  passing  of  the 
disruptive  discharge,  the  positive  column  and  negative  glow  only 
would  have  been  represented,  as  in  Fig.  8. 

The  evidence  thus  far  furnished  appears  to  indicate  con- 
clusively, that  the  positive  column  is  a  channel  in  which  the  air 
is  in  a  condition  of  conduction.  It  is  a  drainage  channel.  The 
positive  terminal  of  the  machine  is  an  exhaust  terminal.  Mole- 


FIG.  15. 

cules  of  air  in  contact  with  it  deliver^negative  corpuscles  to  it. 
Normally  they  are  moving  with  an  average  velocity  of  about  1400 
feet  per  second.  They  are  also  oscillating  to  and  fro  in  the  short 
spark-gaps.  The  corpuscular  nebula  within  the  metal  conductors 
is  set  into  a  rhythmical  vibration.  These  conditions  result  in  a 
delivery  of  negative  corpuscles  to  the  positive  terminal  by  some 
of  the  gas  molecules  which  collide  with  it  at  the  instant  when  the 
terminal  is  in  a  condition  of  maximum  exhaust.  The  same  con- 
ditions result  in  a  rhythmical  issue  from  the  negative  terminal,  of 
negative  corpuscles,  which  are  loaded  upon  the  air  molecules  then 
in  collision  with  that  terminal.*: 

It  is   sometimes   stated   that  X-rays   and    ultra  violet   light 


Conduction  in  Gases  13 

ionize  the  air  and  put  it  in  a  condition  of  conduction.  The  evi- 
dence that  it  is  in  this  condition  is  that  an  electrometer,  the 
metal  parts  of  which  have  either  an  excess  or  a  deficiency  of 
negative  corpuscles,  will  when  placed  in  air  thus  ionized,  re- 
turn to  the  normal  condition.  This  air  thus  ionized  is  not  in 
the  condition  of  air  within  the  positive  column.  In  air  ionized 
by  X-rays,  the  average  negative  charge  per  molecule,  is  the  same 
as  before  the  ionization.  An  overcharged  molecule  will  deliver 
its  excess  of  negative  fluid,  to  the  particular  molecule  which 
it  has  robbed,  to  any  other  molecule,  or  to  a  metal  terminal  in 
a  like  condition.  The  air  which  is  being  repelled  from  a  nega- 
tive terminal,  would  also  deliver  negative  corpuscles  to  an  elec- 
trometer having  less  than  the  normal  charge  of  the  negative  fluid. 
This  would  not  indicate  that  it  is  in  a  condition  of  conduction, 


FIG.   16. 

in  the  sense  in  which  that  word  is  used  in  connection  with^the 
positive  column. 

An  illustration  of  what  is  referred  to  above  as  a  condition 
of  conduction  is  given  in  Fig.  16.  This  is  a  reproduction  of  a 
spark  discharge  over  the  film  of  a  photographic  plate.  Two 
pin-heads  forming  terminals  rested  upon  the  film.  The  points  of 
the  pins  were  soldered  to  the  ends  of  copper  wires,  one  of  which 
was  connected  to  the  negative  terminal  of  the  influence  machine. 
This  line  contained  a  small  spark-gap  of  2  or  3  mm.  The  other 
wire  was  grounded.  The  pin-head  terminals  were  about  7  cm. 
apart.  The  plates  of  the  machine  were  rotated  very  slowly  for 
about  half  a  minute.  In  the  presence  of  the  negative  terminal  the 
a  ir  around  the  grounded  pin-head  was  drained  of  negative  corpus- 


14  Conduction  in  Gases 

cles.  It  was  put  into  a  condition  of  conduction.  The  velocity  of 
rotation  of  the  machine  was  then  increased,  and  a  disruptive  dis- 
charge was  made  to  pass  between  the  pin-heads.  The  air  around 
the  negative  pin-head  was  evidently  not  in  a  condition  of  conduc- 


FIG.  17. 

tion.  A  break-down  of  the  air  was  there  formed.  The  muzzle  of 
the  discharge  channel  thus  formed  was  about  equidistant  from  the 
pin-heads.  A  volley  of  negative  corpuscles  issued  from  this  muzzle . 
Within  the  conduction  region  around  the  grounded  pin-head  there 


FIG.  1 8. 


is  no  definite  outline  for  the  discharge.  It  was  diffused  into  the 
conduction  region  around  the  pin-head.  That  the  shadow  effect 
produced  by  the  lowest  parts  of  the  rounded  pin-head  was  not  due 
to  protection  from  luminous  fogging,  is  made  clear  by  the  form  of 


Drainage  Lines  15 

the  disruptive  part  of  the  discharge,  and  the  direction  of  the 
shadow.  In  many  previous  attempts  to  secure  this  result,  the  dis- 
charge was  practically  along  the  line  joining  the  two  pin-heads, 
and  the  real  explanation  of  this  shadow  effect  was  left  in  doubt. 

Fig.  17  is  a  reproduction  of  a  print  from  the  original  plate 
Fig.  1 6  is  a  reproduction  of  the  original  plate. 

Fig.  1 8  is  a  reproduction  of  a  plate  in  which  the  operation 
described  in  connection  with  Figs.  16  and  17  was  arrested  just 
before  the  disruptive  discharge.  When  the  plate  was  exposed  for 
a  few  seconds  only,  the  effect  of  the  negative  glow  would  be 
appreciable.  Short  drainage  lines  would  also  appear  around  the 


FIG.  19. 

grounded  pin-head.  As  the  time  of  exposure  was  increased,  the 
drainage  lines  became  longer.  It  was  only  after  many  attempts 
that  the  result  shown  in  Fig.  18  was  obtained.  It  was  found 
that  a  disruptive  discharge  usually  occurred,  as  soon  as  the  drain- 
age lines  had  reached  the  negative  glow. 

When  the  pin-head  forming  the  drainage  terminal  is  con- 
nected with  the  positive  terminal  of  the  influence  machine,  as  in 
Fig.  19,  the  drainage  lines  are  much  more  strongly  marked.  In 
Fig.  19  a  single  spark  was  sent  across  two  minute  gaps  at  the 
machine  terminals.  These  gaps  were  between  3  and  4  mm.  in 


i6 


Lightning  Discharges 


••BHBBBl 


FIG.  20.— THE  OVERCHARGED  CLOUD.     An  inflow  of  the  negative  fluid  to  the  main 
discharge  channel,  whose  end  is  seen  at  the  middle  of  the  plate. 


FIG.    21. — THE  OUTFLOW  INTO  THE  CLOUD  WHICH  HAS  LESS  THAN  ITS  NORMAL 

CHARGE. 


Lightning  Discharges  17 

length.  No  luminous  effect  was  observed  on  the  photographic 
plate,  excepting  in  close  proximity  to  the  pin-heads. 

Figs.  20  and  21  appeared  in  a  paper  in  the  January  num- 
ber of  the  Popular  Science  Monthly  for  1912.  The  paper  was  en- 
titled, A  Flash  of  Lightning.  It  was  there  stated  that  Fig.  20 
represents  in  cross-section  a  view  of  a  cloud  which  is  overcharged 
with  the  negative  fluid.  The  end  of  the  long  flash  connecting  this 
with  the  undercharged  cloud,  is  visible  at  the  middle  of  the  plate. 
The  lines  on  this  plate  resemble  a  system  of  rivers  and  tributa- 
ries. They  elongate  up-stream  and  drain  the  negative  fluid  into 
the  long  discharge  channel,  from  which  it  flows  outward  into  the 
undercharged  cloud  at  the  other  end  of  the  flash,  Fig.  21.  This 
last-named  cloud  is  in  a  condition  of  conduction.  The  discharge 
diffuses  into  it.  The  discharge  from  the  first-mentioned  cloud 
is  forked  lightning.  The  discharge  into  the  other  cloud  is  one  form 
of  sheet  lightning.  Before  the  flash  occurred,  the  rain-drops  fall- 
ing through  the  overcharged  cloud  were  all  highly  charged,  and 
they  repelled  each  other.  After  the  discharge  those  drops  which 
happened  to  lie  in  the  path  of  some  one  of  these  tributary  discharge 
lines,  have  lost  their  overcharge.  There  is  then  an  attraction 
between  such  drops  and  those  which  were  slightly  outside  of  these 
drainage  lines,  and  which  are  therefore  still  overcharged.  These 
two  groups  of  drops  are  intimately  commingled,  as  is  shown  by 
the  intricate  nature  of  the  system  of  drainage  channels  in  Fig. 
20.  As  they  continue  their  fall  to  earth,  they  coalesce,  and  a 
brief  dash  of  unusually  large  drops  of  rain  is  observed. 

If  these  discharge  figures  are  to  be  described  in  the  language 
of  the  two-fluid  theory,  Fig.  20  must  be  called  an  outward  positive 
discharge.  Fig.  21  must  be  called  an  outward  negative  discharge. 
We  must  say  that  each  of  these  discharges  come  from  the  cloud  at 
the  opposite  end  of  the  flash. 

Such  an  explanation  seems  so  essentially  absurd  in  the  pres- 
ence of  these  photographic  plates,  that  it  will  not  be  urged. 

In  conclusion,  however,  a  confession  must  be  made.  The 
lightning  discharge  here  described  was  artificially  produced.  A 
plate-glass  machine,  with  metal  conductors  terminating  in  pin- 
heads  took  the  place  of  the  long  flash  of  lightning.  The  pin-heads 
rested  upon  the  centers  of  the  two  photographic  films,  the  plates 
resting  on  large  sheets  of  glass.  There  were  small  spark-gaps  of 


1 8  The  Positive  Column 

about  half  an  inch  in  each  line,  at  the  machine  terminals.  A  single 
spark  across  these  gaps  produced  a  glow  over  the  films  around  the 
pin-heads.  In  order  to  bring  some  of  the  discharge  lines  down  into 
close  proximity  to  the  films,  so  that  they  would  be  sharply  de- 
fined, copper  plates  were  placed  under  each  photographic  plate  be- 
low the  sheet  of  glass.  These  copper  plates  were  grounded  or,  what 
produces  the  same  result,  they  were  connected  with  each  other. 
No  trace  of  the  discharge  can  be  detected  until  the  photographic 
plate  is  developed.  With  this  confession,  and  with  an  apology 
for  having  misled  the  reader,  the  question  may  be  asked,  Can 
any  one  look  at  the  lines  of  Fig.  20,  and  believe  that  they  were 
produced  by  an  outward  discharge  of  positive  electricity? 

Fig.  20  shows  in  addition  to  these  drainage  lines  radial  mark- 
ings which  indicate  the  explosive  conditions  which  exist  within 
any  mass  of  matter  from  which  negative  corpuscles  have  been 
suddenly  drained.  Molecules  of  air  in  contact  with  the  pin-head 
upon  which  the  drainage  lines  centered  were  suddenly  drained  of 
negative  corpuscles.  They  then  repelled  each  other,  and  were 
repelled  by  the  pin-head.  We  might  describe  this  action  by  say- 
ing that  these  positive  ions  are  emitted  from  the  positive  termi- 
nal. We  might  also  say  that  U.  S.  mail-carriers  are  emitted 
from  inhabited  houses,  after  they  have  delivered  the  daily  mail 
matter.  We  might  say  that  the  metal  sphere  which  has  made  con- 
tact with  the  positive  terminal,  becomes  a  positive  ion,  and  is 
emitted  from  the  positive  terminal. 

The  Crookes  tube  has  been  telling  the  whole  story  for  many 
years.  We  have  understood  that  part  of  it  which  referred  to  con- 
ditions at  the  cathode.  The  negative  corpuscles  which  were  capa- 
ble of  operating  the  Crookes  windmill,  evidently  came  from  within 
the  metal  forming  the  cathode.  They  were  emitted  from  the 
cathode  in  straight  lines.  They  did  not  follow  the  windings  of 
the  tube.  Crookes  found  that  in  his  partially  exhausted  tube,  the 
positive  column  started  from  the  positive  terminal  and  curved  to 
the  negative  terminal,  wherever  the  positive  terminal  might  enter 
the  tube.  The  conditions  were  exactly  those  represented  in 
Figs.  6  and  8  of  this  paper.  In  the  experiment  of  J.  J.  Thom- 
son, a  tube  of  irregular  form  and  having  a  length  of  about  50 
feet,  was  filled  throughout  with  the  positive  column.  The  ap- 
pearance at  the  cathode  end  was  exactly  the  same  as  it  would  have 


Interaction  between  Masses  19 

been  if  the  tube  had  been  i  foot  in  length.  Moreover,  as  the 
air  is  exhausted,  and  the  Crookes  condition  is  approached,  the 
positive  column  disappears.  Finally  the  cathode  discharge  only 
remains.  That  the  drainage  lines  elongate  outward  from  the  posi- 
tive terminal  is  no  more  difficult  of  explanation  than  the  fact 
that  the  channel  of  a  stream  elongates  in  the  opposite  direction 
from  the  direction  of  flow.  If  Niagara  Falls  should  recede  from 
Lake  Ontario  to  Lake  Erie  in  a  fraction  of  a  second,  an  observer 
might  get  the  impression  that  there  had  been  a  "discharge"  from 
Lake  Ontario  to  Lake  Erie.  There  is  an  explosive  repulsion  of 
air  molecules  from  both  terminals  when  a  disruptive  spark  passes. 
In  Fig.  19  the  drainage  lines  from  the  positive  terminal  elongate 
toward  the  negative  glow.  But  one  of  them  responds  to  the 
mechanical  effects  involved  in  the  convection  of  overcharged 
molecules.  It  curves  around  the  negative  glow.  Electrically,  the 
molecules  which  are  being  urged  in  opposite  directions  are  friendly. 
Mechanically,  they  oppose  each  other. 

It  is  evident  that  if  matter  could  be  drained  of  its  negative 
corpuscles,  each  atom  and  each  mass  would  repel  every  other 
atom  and  mass.  When  we  attempt  to  do  this,  by  connecting  a 
mass  of  matter  to  the  positive  terminal  of  an  electrical  machine, 
we  find  that  we  can  only  drain  the  negative  corpuscles  from  a  thin 
surface  film.  Molecules  within  a  mass  of  metal  cooperate  with 
each  other  in  retaining  possession  of  the  corpuscular  nebula 
within  it.  The  electrical  pump  leaks.  Drainage  channels  lead- 
ing into  the  air  form  over  the  surface  of  the  mass  to  be  drained, 
and  upon  the  positive  terminal  of  the  machine.  Even  under  these 
conditions  electrical  corpuscles  can  be  drained  from  small  masses 
of  matter  in  sufficient  amount  to  cause  them  to  repel  each  other. 

Assume  two  spheres  of  mass  m  and  m' ' .  They  attract  each 
other  with  a  force  Kmmf/r2.  Assume  that  the  spheres  are 
connected  by  means  of  a  flexible  conductor,  and  that  negative 
corpuscles  are  pumped  out  of,  or  forced  upon  the  two  masses. 
A  conditon  will  be  found  for  which  the  attraction  between  these 
two  masses  will  be  a  maximum.  If  the  number  of  corpuscles  in  or 
on  the  masses  be  then  either  increased  or  diminished,  the  attrac- 
tion will  be  less.  With  small  masses  we  can  easily  reduce  the 
attraction  to  zero,  or  make  it  negative.  The  attraction  in  dynes 
between  these  masses  having  radii  RI  andR2  cm.,  and  distant  from 


20  Explosive  State  of  Matter 

each  other  r  cm.,  the  matter  composing  them  having  a  density  p  is 
RiR2  /i6 

A    —  2        A  7T      p      JV   K.1      K.2          -     \    ). 

Here  K  is  the  gravitation  constant  and  V  is  electrical  potential 
in  electrostatic  units.     This  force  will  be  zero  when 

V  =  ~  TTP  VK  RiR2 

O 

For  two  spheres  having  the  size  of  earth  and  moon,  assum- 
ing p  =  5.5  for  both  masses,  their  potential  must  be  raised  to 
1.96  X  io17  volts,  in  order  that  they  shall  cease  to  attract  each 
other.  Rain-drops  having  radii  of  o.i  cm.  if  charged  to  a  poten- 
tial of  0.0031  volt,  will  have  no  attraction  for  each  other. 

We  do  not  know  whether  the  potential  of  the  earth  is  such 
that  its  attraction  for  the  moon  or  for  masses  on  its  surface  is 
a  maximum,  or  not;  we  do  not  know  whether  or  not  the  gravita 
tion  constant,  as  it  has  been  determined,  has  the  value  that  it 
would  have  if  V  were  really  zero  on  the  earth.  Some  of  the  smaller 
masses  in  our  solar  system  appear  to  disobey  Newton's  law. 

It  is  evident  that  when  small  masses  of  matter  are  suddenly 
drained  of  negative  corpuscles,  we  should  expect  explosive  effects 
to  follow.  Such  a  condition  is  produced  when  a  small  metal  wire 
is  placed  in  the  positive  discharge  line,  a  condenser  of  large  capac- 
ity being  connected  with  the  terminals  of  the  machine. 

The  substance  of  a  paper  presented  to  the  American  Philo- 
sophical Society  at  its  annual  meeting,  April,  1913,  by  the  present 
author  is  presented  in  illustration  of  this  point.1 

In  1815  Singer  published  in  the  Philosophical  Magazine2  an 
account  of  experiments  made  in  Holland  by  De  Nelis,  and  repeated 
by  him,  which  illustrated  what  he  called  the  explosive  effects 
of  electricity.  At  that  time  the  one-fluid  theory  was  generally 
held  by  those  familiar  with  electrical  phenomena.  It  was,  however, 
their  belief  that  the  electrical  discharge  came  from  the  positive 
terminal. 

Singer  made  use  of  a  battery  of  jars  having  an  external  tin- 
foil area  of  75  square  feet.  The  positive  terminal  of  this  battery 

lProc.  Am.  Phil.  Soc.,  Vol.  LII,  pp.  283-6. 
zPhil.  Mag.,  Vol.  XLVI,  p  161. 


Explosive  State  of  Matter  21 

was  separated  from  a  terminal  leading  to  a  wire  of  lead  having  a 
diameter  of  o.oi  inch.  This  lead  wire  was  within  a  small  metal 
cylinder  formed  by  boring  a  hole  into  a  metal  rod.  One  end  of  the 
wire  was  in  contact  with  the  bottom  of  the  bore,  the  other  be- 
ing attached  to  a  copper  wire  through  which  the  discharge  was 
sent  to  the  lead  wire.  This  leading-in  wire  was  surrounded  by 
wax,  and  the  lead  wire  was  surrounded  by  oil.  The  lead  wire  was 
exploded  by  each  discharge.  The  metal  cylinder  was  stronger 
than  any  gun  barrel.  It,  however,  was  shattered  by  the  explosive 
effects,  the  leading-in  wire  was  blown  out  and  the  liquid  was 
sometimes  thrown  to  the  height  of  50  feet  when  the  metal  cyl- 
inder did  not  burst. 

At  the  present  time  it  seems  evident  that,  in  these  experi- 
ments, the  lead  wire  was  suddenly  drained  of  its  negative  cor- 
puscles. What  may  properly  be  called  a  rarefaction  wave  was 
sent  along  the  wire.  When  in  this  condition  each  atom  of  lead  re- 
pels every  other  atom.  The  lead  becomes  explosive.  There  are 
heat  effects  involved  also,  which  assist  in  the  separation  of  the 
atoms,  but  which  alone  do  not  seem  capable  of  accounting  for  the 
results. 

It  seemed  to  the  present  writer  that  it  might  be  of  interest 
to  determine  whether  the  explosive  effects  would  be  the  same 
when  the  negative  discharge  was  sent  through  the  wire  as  when  the 
positive  terminal  was  used.  In  the  former  case  a  compression 
wave  is  sent  through  the  corpuscular  nebula  within  the  wire.  The 
repulsion  effects  are  impressed  upon  the  oil  surrounding  the  wire. 
In  the  latter  case  the  nature  of  the  action  seems  to  be  essentially 
different,  as  has  been  pointed  out  above. 

These  compression  and  rarefaction  waves  are  somewhat  like 
those  which  might  be  impressed  upon  a  column  of  water  within  a 
rubber  tube. 

The  wire  was  placed  within  a  glass  tube  as  shown  in  the 
adjoining  figure.  The  internal  diameter  of  various  samples 
varied  between  i  and  2  mm.  The  length  of  the  tube  was  10 
cm.  The  ends  of  the  tube  were  provided  with  copper  lead- 
ing-in wires  fitting  more  or  less  closely  the  bore  of  the  tube  and  to 
which  the  fine  wire  was  attached,  as  shown  in  Fig.  22.  The  walls 
of  the  tube  were  from  i  to  2  mm.  in  thickness.  The  space 
within  the  tube  around  the  wire  was  completely  filled  with 


22  Explosive  State  of  Matter 

coal-oil,  all  air  being  excluded.  The  ends  of  the  tube  and  the 
leading-in  wires  were  sealed  with  sealing  wax,  which  held  the 
leading  wires  in  place  and  secured  these  wires  and  the  glass  tube 
to  supporting  blocks  of  hard  rubber. 

The  source  of  electricity  was  an  influence  machine,  provided 
with  a  condenser  consisting  of  twenty  sheets  of  glass  66  cm.  square, 
each  plate  having  a  tin-foil  coating  30  cm.  square.  These  plate 
condensers  were  connected  in  multiple,  the  tin-foil  area  being 
about  20  square  feet  on  each  side.  A  pivotally  mounted  ground 
contact  could  be  connected  to  either  terminal  of  the  machine.  By 
means  of  a  similar  contact  rod  either  terminal  could  be  connected 
with  one  of  a  set  of  discharge  rods,  provided  with  an  adjustable 
spark-gap  between  the  knobs.  The  other  discharge  rod  was  con- 
nected with  the  water-pipe  system  of  the  building  by  means  of  two 
No.  8  copper  wires  in  multiple.  The  apparatus  shown  in  the 
figure  was  in  this  ground  line.  The  ground  for  the  machine  was  in 


FIG.  22. 

the  yard  outside  of  the  building.  The  results  were  the  same  when 
the  two  grounds  were  thus  independent  as  when  they  were  united. 

The  wire  to  be  exploded,  contained  within  the  glass  tube  of 
the  figure,  was  a  quarter  ampere  fuse  wire,  having  a  diameter 
of  0.115  mm.  A  small  copper  wire  having  a  diameter  of  0.105  mm- 
was  also  used  with  similar  results. 

A  single  discharge  from  either  the  positive  or  the  negative 
side  of  the  condenser  caused  the  tube  of  glass  to  be  shattered 
into  fragments  so  minute  that  their  impact  upon  the  face  of  the 
observer  when  standing  5  or  6  feet  distant,  produced  no  harm- 
ful effect.  On  several  occasions,  when  the  discharge  came  be- 
fore it  was  expected,  their  impact  upon  the  eyes  was  also  harmless. 
No  trace  of  the  metal  wire  could  be  found.  That  no  harm  could 
come  to  the  observer  became  so  apparent  after  a  large  number  of 
experiments  had  been  made,  that  no  attempt  was  made  to  protect 
either  the  face  or  the  eyes.  The  impact  upon  the  eyes  could  be 
felt  at  each  explosion  thereafter. 

The  small  glass  tube  shown  in  the  figure  was  enclosed  in  a 


Explosive  State  of  Matter  23 

larger  tube  having  an  internal  diameter  of  about  half  an  inch.  This 
tube  was  also  enclosed  in  a  strip  of  cardboard.  In  this  way  the 
dust  into  which  the  inner  tube  was  converted  could  be  collected. 
It  could  be  recognized  as  glass  only  on  examination  with  a  pocket 
lens. 

The  effect  of  the  explosion  on  the  outer  tube,  the  ends  of 
which  were  open,  was  found  to  be  in  all  cases  more  marked  when 
the  compression  or  negative  discharge  was  sent  through  the  wire 
than  when  the  discharge  rods  and  wire  were  connected  with  the  posi- 
tive terminal.  In  some  cases  the  rarefaction  wave  would  pro- 
duce no  apparent  effect  upon  the  outer  tube,  while  the  negative 
or  compression  wave  would  crack  it  or  shatter  it  into  three  or 
four  fragments. 

In  order  to  make  comparative  tests,  the  apparatus  shown 
in  the  figure  was  constructed  in  pairs,  the  two  tubes  being  cut 
from  adjoining  parts  of  the  same  glass  tube.  This  was  also  done 
with  the  larger  tubes  which  were  placed  between  the  supporting 
blocks  and  surrounded  the  small  tube  shown  in  the  figure.  In 
some  cases  two  fuse  wires  or  one  fuse  wire  and  one  copper  wire 
were  placed  in  parallel  within  the  tube.  In  this  way  the  ex- 
plosive effects  were  somewhat  varied.  In  all  cases  the  greater 
effects  of  the  compression  discharge  were  so  marked  that  there 
appears  to  be  no  doubt  of  the  result. 

In  order  to  compare  with  these  results  the  heat  effects  of  an 
ordinary  direct  current,  the  wire  was,  by  a  switch  connection, 
subjected  to  the  current  from  a  separately  excited  2  50- volt  dynamo. 
The  expansion  effects  then  resulted  in  forcing  the  oil  out  through 
the  sealing  wax  at  the  ends  of  the  glass  tube.  No  explosive  ef- 
fects were  produced.  The  same  experiment  was  repeated  by 
switching  the  lead  wire  into  a  ground  line  attached  to  a  city  power 
plant,  the  impressed  potential  being  600  volts.  The  results  were 
exactly  the  same  as  in  the  previous  case,  so  far  as  explosive  effects 
were  concerned.  The  wire  was  fused  and  partly  converted  into  a 
fine  powder  in  both  cases.  The  conditions  here  discussed  should 
be  considered  in  connection  with  the  results  shown  in  Fig.  16. 

When  the  solid  conductor  is  larger  in  cross-section,  the  positive 
terminal  of  a  machine  can  be  in  this  explosive  condition  only  in  a 
thin  film  over  its  surface  and  under  special  conditions  artificially 
produced.  The  fact  that  molecules  of  matter  when  thus  suddenly 


24  Dark  and  Luminons  Columns 

drained  of  negative  corpuscles  becomes  explosive  has  great  signifi- 
cance. It  indicates  that  if  this  were  done  for  all  matter,  it  would 
become  unstable  or  explosive.  Atoms  and  planets  would  repel 
other  atoms  and  planets.  The  cohesion  of  liquids,  the  tenacity 
of  solids,  and  the  gravitational  attraction  between  cosmical  masses, 
would  be  lost  in  universal  repulsion,  which  each  atom  would  have 
for  every  other.  The  behavior  of  radio-active  matter  indicates 
that  it  may  be  on  the  border  line. 

If  the  conclusions  thus  far  reached  are  valid,  they  lead  us 
to  an  explanation  of  the  conditions  within  a  brush  discharge  be- 
tween positive  and  negative  terminals. 

Negative  corpuscles  issue  from  within  the  cathode.  If  the 
air  around  it  is  in  a  condition  approaching  that  in  a  Crookes  tube, 


FIG.  23. 

the  molecules  of  air  are  beaten  back  from  the  cathode.  The 
Crookes  dark  space  is  thus  formed.  Collision  of  these  corpuscles 
with  molecules  thus  beaten  away  from  the  cathode,  produces  the 
luminous  glow,  known  as  the  negative  glow.  If  the  air  pressure 
within  the  vacuum  tube  is  increased  the  Crookes  dark  space  dis- 
appears. The  negative  glow  is  then  in  close  contact  with  the 
cathode.  The  molecules  within  the  negative  glow  being  loaded 
with  an  excess  of  negative  corpuscles,  are  repelled  across  the 
Faraday  dark  space.  They  repel  each  other  electrically,  and  there 
is  no  appreciable  interchange  of  negative  corpuscles  between  them. 
This  interchange  begins  when  they  begin  to  mingle  with  molecules 
within  the  positive  column — the  drainage  column.  If  the  dis- 
charge knobs  are  moved  near  together  (the  condensers  being 
removed)  and  the  conditions  represented  in  Fig.  5  are  imposed, 


The  Hittorf  Tube  25 

Faraday  dark  spaces  invade  the  positive  column.  The  drainage 
streamers  separate  from  each  other.  Convection  and  conduction 
columns  exist  side  by  side.  In  these  columns  the  air  is  being  urged 
in  opposite  directions.  These  columns  jostle  each  other  in  a 
somewhat  tumultuous  way.  The  result  is  that  the  luminous  or 
positive  columns  are  in  the  form  of  concentric  cones,  separated  by 
similar  dark  cones.  Fig.  23  is  a  camera  photograph  of  the  appear- 
ance of  the  positive  knob  when  the  above- described  condition  exists. 
The  exposure  was  so  timed,  that  the  vibrating  luminous  columns  did 
not  develop.  The  exposure  was  followed  by  a  flash-light,  a  re- 
flection of  which  is  shown  upon  the  polished  knob. 


FIG.  24. 

Fig.  24  is  a  similar  reproduction  of  a  negative,  of  the  positive 
knob  taken  through  a  small  hole  in  a  copper  plate,  placed  as  in 
Fig.  8.  The  position  and  arrangement  of  these  dark  and  luminous 
cones,  depends  upon  the  length  of  the  small  spark-gaps  a  and  a1  of 
Fig.  i. 

In  the  Hittorf  tube1  referred  to  by  J.  J.  Thomson,2  a  similar 
condition  exists.  Faraday  dark  spaces  and  positive  columns  are 
joined  to  the  terminals  in  multiple.  The  plan  of  this  tube  is 
represented  in  Fig.  25. 

The  ends  of  the  electrodes  are  only  i  mm.  apart.  The  longer 
tube  joining  the  bulbs  at  the  bottom  of  the  figure  was  in  spiral 
form  and  was  375  cm.  in  length.  Thomson's  description  of  the  be- 
havior of  the  discharge  is  as  follows:  "In  spite  of  the  enormous 
difference  between  the  lengths  of  the  paths,  the  discharge,  when 

1Hittdorf,  Wied.  Ann.,  XX,  p.  704,  1883. 

2  Conduction  of  Electricity  through  Gases,  2nd  ed.,  p.  443. 


26 


Arc-like  Discharges 


the  pressure  was  very  low,  all  went  round  through  the  spiral, 
the  space  between  the  electrodes  remaining  quite  dark." 

The  results  shown  in  Figs.  23  and  24  point  to  a  different  ex- 
planation, as  follows: 

In  the  shorter  branch  of  the  tube,  the  dark  convection  dis- 
charge across  the  Faraday  dark  space  involves  a  transfer  of  super- 
charged gas  molecules  from  cathode  to  anode.  In  the  longer 
branch,  the  electricity  is  passing  by  transfer  from  molecule  to 
molecule,  from  cathode  to  anode.  The  molecules  of  gas  are, 
however,  moving  in  the  opposite  direction.  The  flow  of  gas  in  the 
two  branches  thus  forms  a  continuous  circulation  around  the 
circuit  of  the  two  branches. 


FIG.  25. 

A  similar  condition  exists  when  two  knob  terminals  are 
brought  nearer  than  what  is  known  as  the  critical  spark  length. 
The  dark  convection  discharge  and  the  luminous  or  drainage  col- 
umn then  exist  side  by  side.  The  luminous  column  takes  a  longer 
path,  having  an  arc-like  form.  Thomson  interprets  this  as 
"  showing  that  it  is  easier  to  produce  a  long  spark  than  a  short  one." 
There  is  then  a  dark  convection  discharge  between  the  points  of  the 
knobs  which  are  nearest  together.  This  convection  discharge 
crowds  the  conduction  column  outward.  The  air  molecules  in  the 
dark  and  the  luminous  columns  are  then  moving  in  opposite  direc- 
tions, forming  a  to-and-fro  circulation. 

In  order  to  examine  in  a  somewhat  different  manner  the  condi- 
tions along  wire  conductors  connected  with  either  terminal  of  the 
influence  machine  the  method  here  to  be  described  was  employed. 


High-potential  Lines 


27 


One  terminal  of  the  machine  was  connected  with  an  earth  con- 
nection (Gi,  Fig.  26)  in  the  yard  outside  of  the  building,  a  spark- 
gap  of  i  or  2  cm.  being  made  at  the  machine  terminal.  The 
discharge  from  the  other  terminal  across  a  spark-gap  of  about 


^^f 


FIG.  26. 

30  cm.,  was  led  to  an  independent  ground  (G2)  on  an  adjoining  side 
of  the  building.  The  conductors  in  both  lines  were  No.  8  copper 
wire.  The  line  having  the  long  spark  discharge  through  it  con- 


28  The  Negative  Outflow 

tained  a  high  resistance  R,  near  its  ground  end.  This  resistance 
was  composed  of  three  or  four  strips  of  porous  cloth  bandage, 
placed  in  parallel,  their  ends  being  placed  in  tumblers  of  salt 
water.  This  resistance  could  be  varied  by  changing  the  distance 
between  the  tumblers,  which  rested  upon  glass  supports. 

A  convenient  form  of  resistance  is  obtained  by  threading  one 
or  more  strips  of  the  cloth  bandage  through  a  glass  tube.  The 
ends  of  the  tube  rest  upon  the  brims  of  tumblers,  the  cloth  con- 
ductor dipping  into  salt  water  in  the  tumblers. 

Between  this  resistance  and  the  machine  end  was  inserted 
a  No.  34  copper  wire,  which  passed  horizontally  across  the  film 
of  a  photographic  plate  P,  Fig.  26,  supported  at  its  edges  on  in- 
sulating supports.  This  wire  was  held  in  proper  tension  by  means 
of  brass  springs,  from  which  silk  cords  passed  to  the  wire,  and 
its  position  with  respect  to  the  film  of  the  photographic  plate 
was  adjusted  by  means  of  hard-rubber  supports  on  either  side  of 
the  plate  having  adjusting  screws  of  insulating  material.  Below 
the  center  of  the  plate  a  distance  of  about  1.5  cm.  was  the  pointed 
end  of  a  copper  wire,  which  was  grounded  on  the  water  pipe,  G3. 
The  resistance  R  was  so  adjusted  that  a  spark  discharge  would  not 
pass  from  the  wire  above  the  film  around  the  plate  P  to  the 
grounded  wire  below,  but  would  be  on  the  point  of  doing  so.  This 
adjustment  was  made  for  the  exposures  in  the  positive  and  also  in 
the  negative  line. 

Plate  I  shows  a  5  X  7  inch  photographic  plate  across  which 
5  spark  discharges  from  the  negative  terminal  were  passed.  The 
fine  wire  which  carried  the  discharge  was  in  contact  with  the  film. 
This  wire  was  surrounded  by  a  glow  of  light,  but  the  resistance 
between  the  plate  and  the  ground  was  not  sufficient  to  force  dis- 
charges over  the  film.  To  have  made  this  resistance  greater  would 
have  brought  about  a  spark  discharge  around  the  plate  when  the 
pointed  ground  conductor  was  put  in  position,  although  it  was  not 
in  position  during  this  exposure.  The  effect  produced  by  intro- 
ducing this  ground  wire  Gs  is  shown  in  Plate  II.  This  plate  was 
otherwise  exposed  exactly  as  the  former  plate.  The  ground  wire 
terminated  in  a  pin-point  1.5  cm.  below  the  center  of  the  plate. 
The  result  in  Plate  II  may  be  explained  as  follows: 

i .  By  the  Two-fluid  Hypothesis. — The  negative  discharge  through 
the  wire  in  contact  with  the  film,  is  attended  by  a  positive  dis- 


The  Negative  Outflow  29 

charge  from  the  pin-point  on  the  ground  wire  to  the  lower  face  of 
the  plate.  This  positive  discharge  is  spread  over  an  area  coinci- 
dent with  the  blackened  area  which  the  negative  discharge  is  shown 
to  cover  in  Plate  II.  The  glass  plate  on  which  the  photographic 
film  is  spread  is  in  a  condition  like  that  of  the  glass  wall  of  a 
Leyden  jar  which  has  been  charged  from  the  negative  terminal 
of  the  machine. 

2 .  By  the  One- fluid  Hypothesis. — The  negative  discharge  flowing 
under  compression  through  the  wire  above,  finds  in  the  grounded 
wire  below  a  line  of  leakage.  This  ground  wire  greatly  increases 
the  potential  drop  at  that  point.  A  negative  discharge  from  the 
lower  face  of  the  glass  plate  passes  to  the  pin-point  and  ground 
wire  below.  Simultaneously  a  negative  discharge  from  the  upper 
wire  flows  over  the  film,  and  tends  to  flow  downward  to  the 
ionized  melocules  of  glass  in  the  lower  face  of  the  glass  plate.  It 
constitutes  a  bound  charge. 

These  discharge  effects  can  be  explained  by  either  hypothesis. 
The  photographic  plate  below  and  closely  around  the  wire  in 
Plate  I  is  a  region  of  negative  glow.  Just  outside  is  the  Faraday 
dark  space,  into  which  the  overcharged  molecules  of  air  are  re- 
pelled. These  repelled  molecules  do  not  mingle  with  air  in  the 
condition  in  which  it  is  in  the  positive  column.  Luminous  effects 
exist  only  in  the  immediate  vicinity  of  the  wire,  where  corpuscles 
emitted  from  the  wire  are  loaded  upon  the  molecules  of  air  in 
contact  with  it. 

Plates  III  and  IV  are  reproductions  of  two  photographic 
plates  which  have  been  exposed  in  precisely  the  same  way.  The 
" discharge"  through  the  wire  came  from  the  positive  terminal 
of  the  machine.  The  spark  length  was  about  twice  as  great  as 
the  negative  sparks  used  in  producing  Paltes  I  and  II. 

This  adjustment  could  be  made  without  producing  sparks  of  a 
disruptive  character  over  the  plate  when  the  ground  wire  with 
its  pin-point  terminal  was  placed  below  the  photographic  plate, 
as  was  done  in  Plate  IV.  In  such  exposures  adjustable  spark 
terminals  a  and  &,  Fig.  26,  were  used.  They  were  so  placed  that 
the  negative  discharge  passes  from  a  large  knob  to  a  small  one. 
In  case  of  a  reversal  of  the  electrification  of  the  machine,  the 
adjustable  terminals  are  transferred  to  the  other  terminals  of  the 
spark-gaps. 


The  Negative  Outflow 


PLATE  I.  — NEGATIVE  LINE. 


The  Negative  Outflow 


PLATE  II. — NEGATIVE  LINE.     GROUNDED  POINT  BELOW. 


32  The  Negative  Inflow 

The  streamers  which  surround  the  wires  in  Plates  III  and  IV 
are  the  streamers  of  the  positive  column.  If  they  are  the  result 
of  an  outward  discharge  of  positive  electricity,  the  result  in  Plate 
IV  should  be  similar  to  that  of  Plate  II.  Negative  electricity 
flowing  upward  from  the  grounded  pin-point  to  the  back  side  of 
the  photographic  plate  should  cause  a  condenser  effect.  There 
should  be  an  intensification  of  the  discharge  over  the  film  in  this 
region,  as  in  Plate  II.  The  positive  outflow  there  should  be 
intensified. 

If  these  positive  streamers  are  drainage  lines,  as  prior  evidence 
has  shown  them  to  be,  this  inflow  over  the  film  to  the  wire  should 
be  diminished  over  the  area  lying  above  that  fogged  by  the  nega- 
tive discharge  from  the  grounded  pin-point.  This  is  precisely 
what  occurs. 

The  fogging  in  the  central  part  of  the  plate  is  wholly  due  to  the 
discharge  from  the  pin-point.  This  is  shown  by  the  fact  that  it 
is  not  visible  after  the  plate  has  been  developed  and  before  it  has 
been  fixed,  when  the  plate  is  viewed  from  the  film  side.  It  is 
visible  when  the  film  is  observed  from  below.  When  two  plates 
are  used,  one  having  the  film  in  contact  with  the  wire,  and  the 
other  having  the  film  facing  the  pin-point,  the  fogging  effect  is  all 
upon  the  lower  plate,  if  the  exposure  is  of  the  character  given  in 
Plate  IV.  With  long-continued  exposure  or  with  a  larger  con- 
denser, the  upper  film  may  be  slightly  fogged  through  the  two 
glass  plates. 

The  result  shown  in  Plate  IV  appears  to  be  wholly  inconsistent 
with  the  two-fluid  theory. 

Another  experiment  which  strongly  favors  the  one-fluid  theory, 
was  described  by  the  author  in  1900,  in  a  paper  entitled,  "On 
Certain  Properties  of  Light-struck  Photographic  Plates."1  The 
phenomenon  described  has  some  resemblance  to  what  has  been 
called  ball  lightning.  Figs.  8,  9  and  10  of  that  paper  show 
traces  on  a  photographic  film,  made  by  a  slowly  moving  point  of 
light.  The  motion  of  the  point  of  light  was  always  in  the  direction 
of  flow  of  a  negative  discharge,  and  came  from  the  negative  ter- 
minal of  an  influence  machine.  A  metal  disc  having  a  diameter 
of  a  centimeter  was  armed  with  a  pin-point.  The  point  was  bent 
over  so  that  when  the  disc  was  placed  on  the  film,  the  point  made 

1  Trans.  Acad.  of  Sc.  of  St.  Louis,  Vol.  X,  No.  6. 


The  Negative  Inflow 


33 


PLATE  III. — POSITIVE  LINE. 


34 


The  Negative  Inflow 


PLATE  IV. — POSITIVE  LINE.     GROUNDED  POINT  BELOW. 


Ball-lightning  Effects  35 

intimate  contact  with  the  film.  The  point  rested  upon  a  short 
pencil  mark  on  the  film.  A  slight  moistening  of  the  pencil  mark 
is  of  advantage.  The  knobs  of  the  machine  should  be  widely 
separated,  and  it  is  of  advantage  to  place  a  large  sheet  of  glass 
midway  between  them,  so  that  no  disruptive  discharge  may  occur. 
The  disc  is  to  be  in  metallic  connection  with  the  negative  terminal. 
A  point  of  light  emerges  from  the  pin-point  on  the  pencil  mark,  and 
moves  slowly  over  the  film,  curving  toward  the  positive  terminal 
of  the  machine,  and  leaving  a  darkened  trail  behind.  Along  this 
trail  an  invisible  negative  flow  is  taking  place,  as  can  be  seen  by 
bringing  near  to  it  a  device  which  has  earned  the  name  of  "teazer." 
This  consists  of  two  pins,  tied  or  soldered  together  at  their  head 
ends,  the  points  being  in  opposite  directions.  This  is  mounted 
at  its  middle  point  by  means  of  sealing  wax,  to  a  long  tube  of  glass. 
One  of  these  points  when  presented  to  the  pin-point  on  the  disc 
will  usually  start  the  ball  discharge,  if  it  fails  to  appear. 

It  was  found  to  be  impossible  to  obtain  these  ball  discharges 
from  the  positive  side  of  the  machine.  When  the  teazer  was  used, 
these  discharges  would  come  from  the  point  on  the  teazer  and 
would  move  toward  the  positive  terminal.  Plate  V  of  this 
present  paper  shows  such  discharges.  At  the  top  of  the  figure 
were  placed  two  discs  armed  with  pins,  which  were  connected  to 
the  -f-  and  —  terminals  of  the  machine.  Below  were  two  similar 
discs  opposite  to  those  above  mentioned,  mounted  on  the  same 
photographic  plate,  which  was  10  X  12  inches  in  size.1  These 
discs  were  in  metallic  connection  with  two  large  gas  torches  hung 
on  insulated  supports  in  the  air  outside  the  building.  The  torches 
were  fed  by  means  of  long  rubber  tubes,  ending  in  short  metal 
pipes  to  which  the  line  wires  were  soldered.  Ball  discharges  came 
one  after  the  other  from  the  negative  terminal,  some  of  which  went 
to  the  torch  terminal  opposite,  some  turning  toward  the  positive 
terminal  of  the  machine.  Ball  discharges  also  appeared  from  the 
torch  opposite  the  positive  terminal  and  went  to  that  terminal. 
The  plate  was  exposed  and  developed  in  daylight,  the  developer 
being  hydrochinone,  which  was  weak  in  sodium  carbonate. 
Similar  results  may  be  obtained  by  replacing  the  torches  by  metal 
wires,  each  being  armed  with  about  500  pin-points.  The  black 

1  Separate  plates  for  the  +  and  —circuits  permit  them  to  be  more  widely  sepa- 
rated, and  give  better  results.     Smaller  plates  may   then  be  used. 


36  Ball-lightning  Effects 

lines  on  the  film  are  shown  even  when  the  plate  is  fixed  without 
being  developed.  The  discharges  are  not  discharges  through 
the  air  or  over  the  surface  of  the  film.  They  are  within  the  body 
of  the  film  itself,  and  the  film  shows  a  distinct  depression  along  the 
discharge  lines. 

These  effects  may  be  produced  between  the  terminals  of  the 
machine,  without  any  ground  lines.  Similar  and  much  larger  ball 
discharges  may  be  made  on  a  surface  of  wood  by  means  of  a 
powerful  spark-coil  operated  by  a  direct  current  with  a  Wehnelt 
interrupter.  If  an  alternating  current  is  used  in  the  primary, 
ball  discharges  may  be  obtained  from  both  terminals  simultane- 
ously. They  may  be  led  into  various  paths,  but  cannot  be 
brought  together.  'The  tracks  are  burned  into  the  wood,  and  are 
2  or  3  mm.  in  breadth. 

A  Crookes  tube  may  be  placed  in  either  of  these  discharge 
lines,  from  the  terminals  of  an  influence  machine,  both  lines  being 
carried  to  independent  ground  contacts.  If  placed  in  the  positive 
line,  the  cathode  terminal  of  the  tube  must  be  turned  to  the 
ground. 

This  ground  may  be  on  a  torch,  or  in  a  many-pointed  conduc- 
tor, or  the  cathode  may  be  grounded  directly  on  a  water  pipe. 
Equally  good  X-ray  pictures  may  be  obtained  in  the  positive  or  in 
the  negative  lines,  with  equal  times  of  exposure.  When  placed 
in  the  positive  line,  however,  the  tube  seems  to  operate  in  a  less 
positive  manner  than  when  operating  in  the  negative  line.  When 
this  was  first  done  by  the  author  in  1902,  the  behavior  of  the  tube 
and  discharge  line  created  the  suspicion  that  there  was  a  condition 
in  this  line  which  was  in  the  nature  of  a  rarefaction.  Elec- 
tric discharges  from  all  surrounding  objects  seemed  to  be  flowing 
in  upon  the  tube  and  the  positive  line.  These  objects  were  tipped 
with  brush  discharges.  The  cathode  discharge  seemed  to  be 
somewhat  unsteady  and  was  easily  disturbed  by  the  movement 
of  near-by  objects.  Attention  was  called  to  this  phenomenon  and 
to  the  "ball -lightning"  discharge  in  a  paper  before  the  International 
Congress  of  Arts  and  Science  in  1904. 

This  behavior  of  the  Crookes  tube,  in  connection  with  the 
phenomenon  which  resembles  the  ball  lightning  discharge,  caused 
me  to  make  the  experimental  study  of  electric  discharge  the  results 
of  which  are  presented  in  this  volume. 


37 


4 

V 


r 


PLATE  V. — BALL  LIGHTNING  DISCHARGES. 


38  The  Rowland  Experiment 

We  may  now  give  attention  to  the  metal  conductor  through 
which  a  discharge  passes. 

Rowland's  experiment  on  electrical  convection,1  made  in  the 
laboratory  of  Helmholtz,  showed  that  a  positively  charged  wire 
moved  longitudinally  in  either  direction,  and  a  negatively  charged 
wire  moved  in  an  opposite  direction,  would  produce  the  same 
electro-magnetic  field.  If  the  two-fluid  theory  is  in  accordance 
with  the  facts,  then,  if  the  external  field  is  impressed  upon  a  metal 
wire,  which  is  free  to  move,  positive  and  negative  discharges  should 
be  urged  in  opposite  directions,  and  the  wire  should  remain  at  rest. 

On  the  other  hand,  assuming  the  one-fluid  theory,  the  wire 
itself  is  a  solid  aggregation  of  positive  ions.  It  is  a  positive 
column.  It  should  be  urged  in  a  direction  opposite  to  that  of  the 
negative  discharge. 

A  copper  wire  50  cm.  in  length  and  having  a  diameter  of  0.23 
mm.  was  placed  in  a  glass  tube  supported  at  its  middle  point  in 
a  horizontal  position.  Tubes  of  various  internal  diameters  be- 
tween i  and  5  mm.  have  been  used,  and  all  give  similar  results. 
The  length  of  the  tube  is  such  that  the  wire  protrudes  from  it  at 
each  end,  a  distance  of  5  or  6  cm.  The  ends  were  bent  down- 
ward at  right  angles  to  the  horizontal  part  of  the  wire,  in  order 
to  eliminate  end  effects. 

Two  discharge  knobs  forming  the  terminals  of  rods  2.5  meters 
in  length  were  placed  with  their  centers  over  the  ends  of  the 
glass  tube.  The  rods  were  supported  near  the  glass  tube  by  silk 
cords.  The  other  ends  rested  on  the  discharge  rods  of  an  influence 
machine  driven  by  an  electric  motor.  It  is  of  advantage  that 
the  knobs  be  placed  above  the  ends  of  the  tube.  The  protruding 
ends  of  the  wire  are  slightly  lifted  just  before  the  sparks  occur. 
This  prevents  bending  of  the  wire  around  the  edge  of  the  glass  at 
the  end  of  the  tube,  from  interfering  with  the  longitudinal  creep- 
ing of  the  wire. 

The  discharge  gaps  at  the  ends  of  the  glass  tube  were  made 
equal.  The  discharge  knobs  had  equal  diameter.  The  gaps 
usually  had  a  length  of  4  or  5  cm.  each,  so  that  discharges 
could  be  freely  produced,  at  intervals  varying  from  half  a  second 
to  three  seconds. 

The  experiment  was  varied  by  suspending  the  wire  on  three  or 

1  Am.  Jrl.  of  Sc.  [3],  XV,  30-38,  1878.     Physical  Papers  of  Rowland,  p.  128. 


The  Rowland  Effect  Reversed 


39 


four  silk  fibers.  One  was  attached  at  the  middle  of  the  wire,  the 
others  a  couple  of  inches  inside  of  the  spark  terminals.  These 
terminals  were  in  the  form  of  rings  which  closely  encircled  the  wire. 
These  rings  were  at  the  ends  of  brass  rods  lying  in  the  same  hori- 
zontal plane  as  the  wire,  and  leading  to  the  machine  terminals 
about  10  feet  distant. 

The  air  in  the  room  must  be  very  quiet,  in  order  to  prevent  its 
effect  upon  the  suspending  fibers  of  silk.  Such  circulation  as 
exists  in  a  room  heated  by  warm  air  interferes  with  the  result. 
If  the  wire  is  placed  in  a  tube  as  in  Fig.  27  referred  to  above,  the 
tube  may  be  divided  in  half,  and  a  pointer  consisting  of  a  fine  fiber 
of  glass,  or  a  silk  fiber,  may  be  attached  to  the  wire  between  the 


FIG.  27.— APPARATUS  SHOWING  THE  GRADUAL  CREEPING  or  A  WIRE  IN  A  DIREC- 
TION OPPOSITE  TO  THE  CORPUSCULAR  DISCHARGE. 

tubes.  This  serves  as  a  mark  upon  which  the  telescope  may  be 
set,  for  observing  the  displacement.  The  support  for  the  glass 
tubes  must  of  course  be  provided  with  leveling  screws. 

The  spark  discharges  used  were  from  two  large  Leyden  jars. 
Larger  condensers  may  disturb  the  result  by  causing  a  wire  of  this 
size  to  buckle. 

It  was  found  that  the  wire  did  not  appreciably  move  when  any 
spark  discharge  passed  through  it.  When  lying  in  the  glass 
tube,  after  six  or  eight  discharges  had  been  made,  it  could  be 
seen  that  the  wire  had  moved. 

When  the  direction  of  the  discharge  was  reversed,  and  leveling 
adjustments  had  been  made,  the  wire  crept  in  the  opposite  di- 
rection. This  operation  has  been  continued  for  hours.  In  one 
case  in  which  3500  discharges  were  made,  the  wire  moved  over  a 
distance  of  1.2  cm.  A  plate-glass  condenser  was  used,  the  area 


40  Shadow  Images 

of  the  brass  sheet  on  each  side  being  about  1000  sq.  cm.  When  the 
wire  was  hung  on  silk  fibers,  summation  effects  were  obtained,  by 
means  of  brushes,  each  composed  of  4  or  5  hairs  from  the  tail  of  a 
horse.  They  were  mounted  in  a  vertical  position  on  blocks  of 
rubber  resting  on  a  plate  of  glass.  The  brushes  were  moved  into 
contact  with  the  sides  of  the  wire.  The  contact  was  just  sufficient 
to  prevent  the  wire  from  moving  backward  after  the  faint  displace- 
ment due  to  each  discharge  was  obtained.  On  many  occasions 
the  wire  was  apparently  prevented  from  moving,  by  some  frictional 
contact,  or  irregularity  of  surface,  which  could  not  be  detected. 
A  slight  displacement  would  then  remedy  the  trouble.  In  a  few 
cases  where  the  discharge  had  been  continued  for  hours,  the  wire 
appeared  to  become  less  sensitive.  It  could  not  be  made  to  move. 
When  left  in  this  position  for  a  day  or  two,  it  at  once  responded 
by  moving  as  if  it  were  a  positive  column.  These  results  suggest 
that  there  may  be  fatigue  effects  involved.  Such  results  were  ob- 
tained by  accident  in  a  sheet  of  hard  rubber.  Five  fibers  of  red 
glass  had  been  mounted  upon  a  frame  of  hard  rubber.  The  fibers 
were  laid  upon  the  film  of  a  photographic  plate  and  placed  in  a 
holder  of  hard  rubber.  This  holder  was  placed  upon  a  sheet  of 
glass  below  which  was  a  metal  sheet  serving  as  the  positive 
plate  of  a  condenser.  The  other  metal  plate  was  placed  above 
the  holder.  It  was  supported  by  blocks  of  hard  rubber,  so  that  it 
was  lifted  slightly  above  the  hard-rubber  plate-holder.  One 
hundred  spark  discharges  were  sent  across  the  machine  terminals 
to  which  the  condenser  was  attached.  The  spark  length  was  about 
30  cm.  Shadow  images  of  the  glass  fibers  were  produced  on  the 
photographic  film,  such  as  are  produced  by  Rontgen  rays. 

In  Fig.  28  such  shadow  images  were  produced,  but  in  this 
instance  the  glass  fibers  had  been  left  out  by  mistake.  The  fi- 
bers had  been  on  another  photographic  film,  which  had  been  pre- 
viously exposed  in  the  same  holder. 

These  shadow  images  are  therefore  due  to  glass  fibers  which 
had  never  been  in  contact  with  this  photographic  film.  Their 
prior  presence  in  the  same  holder  on  another  film,  had  resulted 
in  producing  after-effects  in  the  hard-rubber  cover.  This  figure 
also  shows  fainter  images  of  the  glass  fibers  in  the  position  they 
had  been  in  during  a  still  earlier  exposure,  the  hard  rubber  frame 
on  which  the  fibers  were  mounted  having  been  reversed  in  position. 


Fatigue  Effects  41 

Fig.  28  is  a  reproduction  of  the  original  plate.  A  shadow  of  the 
hard-rubber  frame  on  which  the  fibers  were  mounted  is  also  shown 
around  the  edges  of  the  figure. 

When  the  holder  was  opened  and  it  was  discovered  that  it 
contained  nothing  which  could  produce  a  shadow  picture,  the  first 
impulse  was  to  deposit  it  in  a  scrap-heap  in  which  thousands  of 
other  plates  had  been  placed,  by  reason  of  their  non-instructive 
character.  The  idea  of  after-effects  suddenly  presented  itself,, 
and  the  accident  was  made  useful.1 


FIG.  28. 

Another  question  which  has  received  attention  in  the  past 
is  the  velocity  with  which  the  electric  fluid  moves  in  the  con- 
ducting wire.  On  this  subject  Maxwell  makes  this  statement:2 

"As  to  the  velocity  of  the  current,  we  have  shown  that  we 
know  nothing  about  it,  it  may  be  the  tenth  of  an  inch  in  an  hour, 
or  a  hundred  thousand  miles  in  a  second.  So  far  are  we  from 

1  This  result  led  to  a  report  that  in  taking  a  photograph  of  the  interior  of  a  room,, 
the  photograph  of  a  man  had  been  obtained  who  was  not  in  the  room  at  the  time 
when  the  photograph  was  taken,  but  who  had  been  there  on  a  former  occasion. 

2  Electricity  and  Magnetism,  II,  p.  197,  1881.-  , 


42  An  Electrical  Pumping  Service 

knowing  its  absolute  value  in  any  case,  that  we  do  not  even  know 
whether  what  we  call  the  positive  direction  is  the  actual  direction 
of  the  motion  or  the  reverse." 

In  1895  the  present  writer  made  a  suggestion,  which  is  of 
interest  in  this  connection,  although  it  does  not  give  any  grounds 
for  a  decision  of  the  question  which  Maxwell  suggests.1  It  does 
suggest  that  the  velocity  of  flow  is  greater  than  an  inch  in  an 
hour. 

Imagine  two  conducting  spheres  having  radii  equal  to  that 
of  the  earth,  or  6.37  X  io8  cm.  Let  them  be  charged  to  potentials 
+  25  and  —  25  volts.  Connect  them  with  a  wire  containing  in 
circuit  a  5o-volt  i-ampere  lamp,  the  resistance  of  the  wire  con- 
ductor being  neglected.  In  order  to  maintain  the  potential  dif- 
ference on  the  two  spheres  constant,  and  thus  maintain  normal 
candle  power  in  the  lamp  while  all  of  this  store  of  electricity  is 
being  used,  the  two  spheres  must  be  forced  to  collapse  to  zero  ra- 
dius at  a  uniform  rate  of  motion. 

Since  —  =  V  we  have 
r 

dQ  =  V  dr  =  i  dt 
or 


i         300     3  X  io9 

The  time  during  which  the  operation  of  the  lamp  could  be 
maintained  by  this  amount  of  electricity  is  therefore  0.035  second. 
We  must  therefore  think  of  this  operation  as  being  continuously 
repeated  28  times  a  second  in  order  to  maintain  a  5o-watt  lamp  in 
normal  operation.  The  velocity  with  which  the  radii  must 
shorten  from  6.37  X  io8  cm.  (4000  miles)  to  zero  during  each 
stroke  of  the  piston  of  this  electrical  pumping  service,  is  1.8  X  io10 
cm.  per  second,  or  about  113,000  miles  per  second.  This  is 
more  than  half  the  velocity  of  light. 

A  discussion  of  a  similar  character  was  made  in  1911,  which 
seems  to  be  somewhat  more  instructive.2 

Suppose  a  copper  wire  of  radius  r  and  length  L  to  be  surrounded 

1  Nipher,  Electricity  and  Magnetism,  p.  390,  §  222. 

2  Nipher,  Trans.  Acad.  of  Sc.  of-  St.  Louis,  Vol.  XX,  p.  12. 


A  Convection  Current  43 

by  a  co-axial   surface  of   radius  r'  '.     The   two  surfaces  form  a 
condenser  of  capacity 


2  loge  p 

where  p  =  — 

Ground  the  outer  shell,  thus  keeping  its  potential  zero. 
Charge  the  wire  core  to  a  potential  V.  Connect  one  end  of  this 
core  to  a  ground  of  infinite  capacity  through  a  resistance 

*  =  r 

ks 

Move  the  condenser  toward  the  resistance  R  with  a  velocity 
v,  and  assume  that  the  condenser-wire  collapses  longitudinally 
at  the  point  where  it  makes  contact  with  the  resistance  R.  The 
velocity  v  is  to  be  so  adjusted  that  the  potential  V  remains  constant 
The  current  delivered  to  the  wire  of  resistance  R  is  then 

.  _  dQ  _      dC  _V_       dL 

dt  dt  2  logep      dt 

The  velocity  with  which  the  wire  must  move  is 
dL  i  i 


From  this  equation  it  would  appear  that  if  the  capacity  of  the 
condenser  per  unit  length  is  infinite  or  p  =  i,  the  velocity  v 
will  be  zero  if  R  >  o. 

On  the  other  hand  if  the  velocity  v  were  made  equal  to  that 
of  light,  R  being  in  electrostatic  units 


=   2  3  X  io10R 
If  R  is  measured  in  ohms 

0.434294  X  3  X  io10  X  io9 
°gl°  P  =  ~2  X  9  X  io™~ 

=  0.007235  R 
The  values  of  p  for  various  values  R  are  given  in  Table  I. 


44 


A  Convection  Current 


TABLE  I 

v  =  3  X  io10 

R  ohms 

P 

O.I 

i  .0 

IO.O 

i  .0016 
i.  0168 
1.181 

IOO.O 

5.290 

TABLE  II 

p  =  i.  0016 

R  ohms 

•o 

O.  I 
I  .0 
IO.O 
IOO.O 

3.00  X  io10 
3.00  X  io9 
3.00  X  io8 
3  .00  X  io7 

If  the  value  of  p  be  made  1.00164+  as  in  the  case  given  in 
the  first  line  of  Table  I,  the  value  of  v  for  the  various  values  of 
R  are  given  in  Table  II.  The  current  delivered  will  of  course 
depend  on  the  value  V. 

The  quantity  of  electricity  per  unit  length  of  the  condenser 
core  is 


dQ 
dL 


V 


2  logep  Rfl  V 

The  current  in  terms  of  the  velocity  v  is  therefore 

.  _      dQ 

;  dL 

If  we  now  consider  the  conditions  within  the  wire  of  resistance 
R,  to  which  this  current  is  being  delivered,  z>'  being  the  velocity 
with  which  the  fluid  flows  in  the  wire,  we  shall  have  an  equation 
similar  to  the  last,  or 


,dQ 


**, 


On  the  condenser  core,  the  convection  current  is  carried  on  a 
thin  film  of  its  surface.  In  the  wire  of  resistance  R,  the  same 
current  is  distributed  uniformly  over  a  cross-section  s.  The 
relation  between  the  conduction  resistance  R  and  what  may  be 
called  the  convection  resistance  is 


2  logep 


^ 
~ks 


When  the  values  of  v  and  p  satisfy  this  equation  the  potential 
of  the  condenser  core  will  be  constant  and  the  current  through  R 


Velocity  of  Electrical  Flow  45 

will  therefore  be  constant.  The  velocities  v  and  vf  will  then  be 
such  as  to  satisfy  the  condition. 

,*2     .*« 

v  dL  dl 

If  the  wire  of  resistance  R  were  now  to  be  replaced  by  one 
having  a  length  2l  and  a  section  2$,  the  current  would  remain 
unchanged.  The  potential  or  electrical  pressure  at  the  end  which 
joins  to  the  condenser  core  would  remain  unchanged.  The  current 
per  unit  cross-section  and  the  drop  in  potential  per  unit  length 
will  be  half  as  great  as  before.  If  we  are  to  consider  the  amount 
of  moving  electric  fluid  contained  in  i  c.c.  of  the  wire  to  be  the  same 
as  before,  then  v'  will  have  been  reduced  to  half  its  former  value, 

and  -jv  will  have  been  doubled.     It  would  then  require  four  times 

the  time  for  a  given  element  of  the  fluid  to  traverse  the  resistance 
R,  that  was  needed  for  the  wire  of  half  the  length.  This  involves 
an  abrupt  change  in  the  velocity  of  the  corpuscles,  at  the  point 
where  the  cross-section  s  changes,  in  any  circuit.  As  an  illus- 
tration assume  that  a  tube  of  cross-section  S  contains  a  column  of 
sand  of  length  /,  and  in  series  with  it  contains  a  column  of  gravel 
of  length  k.  The  lengths  are  such  that  the  two  columns  have 
equal  resistance  to  the  flow  of  a  fluid  through  them.  We  may  as- 
sume that  the  effective  cross-sections  of  these  columns  are  m  S 
and  jit2  S.  The  current  flowing  through  the  two  columns  is 


where  vi  and  v-2  represent  the  velocity  of  flow.  The  distances 
over  which  the  flow  will  pass  within  these  columns,  during  a  time 
t  will  be 

d\  =  DI  t 
d%  ==  1)2  t 

The  resistance   of   these   two   columns,   neglecting  frictional 
effects  would  be 

/i  k 


r  = 


Ml  3         M2 


Let  the  time  required  for  the  liquid  to  pass  from  end  to  end 
of  the  two  tubes  be  t\  and  /2  then 


46  Velocity  of  Electrical  Flow 


Hence 

^i  _  di  _  h  _  M2 
v2       d%       li       MI 

If  these  columns  of  sand  and  gravel  were  in  multiple,  they 
having  pressures  in  common  at  their  extremities,  as  in  a  divided 
circuit,  equal  quantities  would  enter  and  equal  quantities  would 
leave  during  the  same  time-interval,  the  inflow  and  outflow  be- 
ing equal.  Let  the  two  columns  be  of  the  same  material.  The 
tubes  containing  them  will  then  have  sections  Si  and  S2.  The 
length  /i  and  /2  are  to  be  such  that  they  have  equal  resistance 
to  flow.  Then  in  the  equation  for  z\,  ^i  ~  M2-  In  the  ratios 
which  follow,  82/81  would  replace  M2/Mi- 

The  electrical  conductivity  of  gold  is  about  five  times  that 
of  platinum.  Assume  that  /*2/Mi  =  5-  Then  Vi  =  5^2-  This 
would  mean  that  the  velocity  of  flow  in  platinum  is  five  times  the 
velocity  in  gold  under  the  assumed  conditions.  The  time  required 
for  the  flow  through  the  wire  of  gold  would  be 

M2\2    , 

—  I     /i  =   25/1. 

Ml/ 

The  velocity  of  flow  of  the  fluid  would  in  all  cases  increase 
directly  as  the  quantity  per  second  flowing  through  any  section  of 
the  conductor. 

In  the  equation 

v  R  =  2  loge  p 

if  p  be  given  the  value  assumed  in  Table  II,  and  the  wire  to  which 
the  current  is  to  be  delivered  have  a  resistance  o.i  ohm  the  con- 
vection velocity  of  the  condenser  core  must  be  that  of  light  in 
order  to  maintain  a  constant  current. 

The  capacity  per  unit  length  of  the  condenser  is  independent 
of  its  radial  dimensions.  If  the  inner  core  has  a  radius  of  100  cm., 
that  of  the  surrounding  shell  must  be  100.16  cm. 

The  distance  between  the  two  surfaces  of  the  condenser  would 
be  1.6  mm.  The  copper  wire  having  a  resistance  of  o.i  ohm  may 
be  a  No.  26  wire  B.  W.  G.  having  a  radius  of  0.23  mm.  and  a 
length  of  95.6  cm.  Under  these  conditions  represented  in  the 


Electrical  Striae  47 

first  line  of  Table  II,  the  potential  of  the  inner  core  of  the  con- 
denser would  remain  constant,  whatever  that  potential  might  be. 
The  condenser  would  be  delivering  10  coulombs  per  second  to  the 
wire,  if  the  potential  of  the  condenser  core  were  i  volt,  The 
current  would  be  10  amperes. 

Under  these  conditions  it  seems  difficult  to  believe  that  the 
velocity  of  corpuscular  flow  within  this  wire  could  be  as  small  as 
iV  inch  per  hour. 

We  must  assume  that  when  negative  ^corpuscles  issue  from  the 
cathode  of  the  Crookes  tube  they  are  capable  of  imparting  kinetic 
energy  to  masses  of  matter.  When  converged  to  a  focus  upon  a 
sheet  of  platinum,  they  are  capable  of  producing  a  marked  rise  of 
temperature.  They  produce  similar  effects  when  they  collide 
with  the  positive  carbon  of  an  arc  light.  When  in  the  circuit  of  a 
dynamo,  they  are  forced  out  of  atoms  which  attract  them,  and 
they  enter  adjoining  atoms  which  also  attract  them.  In  doing 
this  they  produce  atomic  vibrations  which  are  apparently  com- 
parable with  those  which  can  be  produced  by  beating  the  conduct- 
ing wire  with  a  sledge  hammer.  When  a  change  in  velocity  takes 
place,  as  a  corpuscular  flow  crosses  the  boundary  between  wires 
composed  of  different  metals,  this  change  results  in  a  change  in 
temperature.  The  specific  heat  of  the  metal  is  one  factor  which 
determines  the  change  in  temperature. 

When  such  a  union  in  a  closed  circuit  is  heated,  one  of  these 
metals  delivers  negative  corpuscles  to  the  other.  Similar  results 
are  produced  when  unlike  substances  are  placed  in  contact,  and 
rubbed  together. 

The  striae  in  the  positive  column  of  the  Geissler  tube  are 
explained  as  electrically  produced  air  waves,  similar  to  those  in 
an  organ  pipe.  The  adjoining  halves  of  a  wave  are  Faraday  dark 
spaces,  and  conduction  columns.  In  these  half-waves,  the  mole- 
cules of  gas  are  moving  in  opposite  directions.  This  involves 
conditions  of  maximum  and  minimum  pressure.  These  changes 
in  pressure  involve  a  change  in  the  conditions  of  conduction,  and 
result  in  a  constant  variation  in  the  position  of  the  striae. 

Vibrations  in  the  spark-gaps  a,  a'-  of  Fig.  i,  impress  waves  in 
the  corpuscular  nebula  within  the  conductors.  Where  the  electric 
fluid  is  under  compression,  the  outer  surface  of  the  wire  is  super- 
charged. Between  these  compression  points  the  surface  of  the 


48  Decomposition  of  Steam 

wire  has  a  deficiency  of  the  negative  fluid.  A  drainage  inflow 
from  the  air  will  here  occur,  such  as  exist?  in  the  positive  "  dis- 
charge." This  is  also  sometimes  known  as  a  coronal  effect. 

It  is  also  evident  that  in  adjoining  semi- waves  the  conditions 
exist  which  tend  to  cause  a  longitudinal  collapse  of  the  wire.  The 
wire  tends  to  become  shorter.  When  large  discharges  are  made 
through  a  wire  of  small  cross-section,  it  buckles  into  waves. 
This  phenomenon  was  apparently  first  discovered  by  Edmund 
Becquerel,  in  1839.  (Pogg.  Ann.  Bd.  48,  S.  546.) 

After  the  manuscript  of  this  volume  was  sent  to  the  publisher, 
an  attempt  was  made  to  apply  a  reversal  of  the  Rowland  effect  to  a 
column  of  distilled  water. 

Two  beakers  each  having  a  capacity  of  1/2  liter  were  partly 
filled  with  distilled  water,  which  had  been  freshly  boiled.  The 
water  in  the  two  vessels  was  connected  by  means  of  a  glass  tube 
forming  a  siphon.  Platinum  terminals  connected  with  long  rods 
leading  to  the  knobs  of  the  influence  machine  were  inserted  in  the 
two  vessels. 

It  was  found  that  when  the  machine  was  in  action,  the  water 
was  urged  from  the  beaker  at  the  positive  terminal,  into  the  other 
beaker  A  difference  in  level  of  about  3.8  mm.  was  produced. 
There  were  small  spark  gaps  at  the  machine.  There  were  no 
condensers  attached. 

The  siphon  above  described  was  replaced  by  one  formed  of  a 
capillary  tube,  having  an  internal  diameter  of  about  0.2  m.m. 
other  conditions  being  unchanged.  The  same  results  were  ob- 
tained. The  movement  of  the  water  in  the  siphon  was  now  made 
apparent.  The  water  column  was  broken  into  segments.  Bubbles 
of  vapor  formed  in  it.  They  moved  toward  the  negative  end  of 
the  tube.  In  order  to  maintain  this  flow  the  water  level  in  the 
beaker  at  the  positive  end  of  the  siphon  was  raised  2  or  3  cm.  above 
that  in  the  other  vessel.  It  soon  became  evident  that  water  was 
being  decomposed  within  the  bubbles  of  vapor.  The  gases  dis- 
charged from  the  tube  were  collected.  The  mixture  was  explosive. 
The  two  platinum  wires  were  enclosed  by  tubes  of  glass  filled  with 
water,  the  wires  entering  at  the  tops  of  the  tubes.  In  this  way  the 
hydrogen  and  oxygen  liberated  at  the  electrodes  was  also  collected. 
It  was  found  that  the  amount  of  water  decomposed  in  the  capil- 


Decomposition  of  Steam 


49 


lary  tube  within  the  bubbles  of  vapor,  was  vastly  greater  than  that 
decomposed  at  the  electrodes  during  the  same  time  interval. 

In  one  case  during  10  hoars  of  operation  9.5  cu.  cm.  of  explosive 
gas  was  discharged  from  the  capillary  tube,  while  the  volume  of 
oxygen  and  hydrogen  collected  at  the  electrodes  was  o.  18  cu.  cm. 
In  the  same  circuit,  the  same  discharge  decomposed  more  than 
fifty  times  as  much  water  by  impact  within  the  vapor,  as  was 
decomposed  by  it  within  the  liquid  by  electrolysis. 

On  one  occasion,  before  accurate  means  for  the  measurement  of 
the  volumes  had  been  secured,  it  was  estimated  that  about  800 
times  as  much  water  was  decomposed  in  the  capillary  tube  as  at 
the  electrodes.  For  a  machine  of  given  output,  the  cross-section 

0  HO  H 


Hlh 


FIG.  29. — WATER  DECOMPOSED  WHEN  IN  THE  FORM  OF  VAPOR. 

of  the  tube  is  an  important  element  in  the  result.     Unless  bubbles 
of  vapor  form  in  the  tube,  no  water  will  be  decomposed  in  it. 

It  was  also  found  that  the  siphon  was  urged  in  the  same 
direction  as  was  the  water  column.  It  would  slide  upon  the  brims 
of  the  beakers  over  a  distance  of  2  or  3  cm.  in  a  fracton  of  a 
second.  It  was  necessary  to  hold  it  in  position. 

The  beakers  were  replaced  by  glass  tubes,  which  were  connected 
by  means  of  the  capillary  tube,  the  electrodes  entering  at  the 
outer  ends  as  shown  in  Fig.  29.  The  large  tubes  were  closed  by 
means  of  four  rubber  stoppers,  which  held  the  electrodes  and  the 
capillary  tube  in  place. 

Similar  results  were  thus  obtained.     The  siphon  arrangement 


50  Evaporation  and  Electrical  Condition 

has  been  found  to  be  the  more  satisfactory.  Complications  arise 
from  the  breaking-down  of  the  rubber  stoppers,  and  from  bending 
stresses  in  the  capillary  tube  forming  part  of  the  service  shown  in 
Fig.  29. 

There  are  indications  that  evaporation  from  the  surfaces  of  the 
water  in  the  two  beakers  is  increased  by  the  electrification.  The 
surf  ace  film  of  water  in  the  positive  beaker  is  in  a  slowly  explosive 
condition.  The  air  around  it  is  in  a  condition  approaching  satura- 
tion. A  cloud  of  tobacco  smoke  around  it  causes  a  marked  deposit 
of  water  upon  the  vessel  and  the  capillary  tube.  It  flows  along  the 
horizontal  part  of  the  tube  when  the  negative  terminal  of  the 
machine  is  grounded.  It  falls  in  drops  between  the  two  beakers 
and  flows  down  the  wall  of  the  beaker  at  the  negative  or  grounded 
end.  The  distance  between  the  beakers  was  about  10  cm. 

The  siphon  was  removed,  and  the  beakers  were  replaced  by 
earthenware  plates,  and  an  attempt  was  made  to  examine  the 
temperature  of  the  water  during  evaporation.  Two  thermometers 
were  dipped  into  the  water.  The  column  of  mercury  in  the  ther- 
mometer placed  in  the  water  at  the  positive  terminal  was  parted 
at  the  bulb,  and  the  entire  column  was  driven  to  the  top  of  the  tube, 
A  luminous  column  was  visible  in  the  vacant  space  thus  formed 
within  the  tube.  Nothing  of  this  kind  happened  to  the  other 
thermometer.  The  evaporation  in  both  plates  is  greater  than  that 
which  takes  place  during  the  same  time  from  plates  not  connected 
with  the  machine.  The  water  which  is  connected  with  the  posi- 
tive terminal  evaporates  more  rapidly  than  that  in  the  plate  con- 
nected with  the  negative  terminal.  Of  course  neither  terminal  of 
the  machine  is  to  be  grounded  in  this  case.  This  work  will  receive 
attention  during  the  coming  year.  The  statements  here  made  are 
apparently  based  on  conclusive  evidence,  but  the  subjects  dis- 
cussed in  this  after-note  require  additional  investigation. 


Causes  of  Local  Magnetic  Storms 

The  work  of  Ampere  nearly  a  century  ago,  taken  in  connection 
with  the  fact  that  fragments  of  a  steel  magnet  are  also  magnets, 
was  sufficient  grounds  for  the  theory  that  the  molecules  of  mag- 
netic matter  may  contain  closed  electrical  currents.  The  dis- 
covery of  the  electron  gave  additional  weight  to  the  older  sugges- 
tion. With  a  view  of  obtaining  direct  evidence  of  this  condition 
within  a  steel  magnet,  the  writer  began  a  series  of  experiments 
which  have  led  to  interesting  results,  but  which  leave  the  original 
question  unanswered. 

It  appeared  possible  that  the  magnetic  force  of  a  steel  magnet 
might  be  diminished  by  draining  negative  electrons  from  it.  This 
was  done  by  connecting  it  with  the  positive  terminal  of  an  influence 
machine. 

The  magnet  to  be  tested  was  30  cm.  in  length  and  about  2.5 
cm.  in  diameter.  It  was  composed  of  a  thin  film  of  steel  0.2  mm. 
in  thickness.  It  was  formed  of  a  single  layer  of  steel  wire  wound 
longitudinally  on  a  piece  of  rubber  hose,  rendered  rigid  by  means 
of  a  core  of  wood.  The  winding  was  in  the  form  given  the  copper 
windings  of  a  drum  armature.  The  wire  was  held  in  place  by  silk 
cord,  and  the  steel  wire  crossing  the  ends  of  the  hose  was  removed. 
The  wire  was  then  magnetized. 

This  wire  magnet  was  used  as  a  deflecting  magnet,  being 
placed  at  right  angles  to  a  needle  suspended  on  a  silk  fiber.  The 
needle  was  wholly  enclosed  in  a  metal  shield.  A  mirror  attached 
to  the  suspension  was  observed  through  a  glass  window  covered 
with  copper  wire  gauze.  A  telescope  and  scale  was  used  in  ob- 
serving deflections,  i  mm.  having  an  angular  value  of  $'.4. 
The  deflecting  effect  of  the  wire  magnet  was  balanced  by  a  large 
bar  magnet  placed  on  the  opposite  side  of  the  needle.  The  needle 
was  rendered  sensitive  to  changes  in  the  turning  moment  of  the 
wire  magnet,  by  partially  compensating  the  effect  of  the  earth's 
field  by  means  of  bar  magnets  on  either  side  of  the  needle.  The 
time  of  a  complete  vibration  in  the  earth's  field  within  the  building 

51 


52  Artificial  Magnetic  Storm 

was  the  same,  when  all  magnets  were  removed  as  when  the  op- 
posing deflection  magnets  were  in  place,  namely,  8.94  seconds. 
The  compensating  magnets  increased  the  vibration  period  to  20 
seconds. 

It  was  found  when  either  terminal  of  the  influence  machine 
in  an  adjoining  room  was  connected  with  the  insulated  wire  mag- 
net, the  other  terminal  being  grounded,  that  the  deflecting  effect 
of  this  magnet  was  increased.  The  angle  of  deviation  could  not 
be  determined  with  any  precision,  on  account  of  fluctuations  in 
the  needle,  but  it  amounted  to  about  15  minutes  of  arc.  In 
some  of  the  earlier  experiments  the  reverse  result  was  obtained. 
It  was  then  concluded  that  the  attraction  between  magnets,  like 
that  between  masses  of  matter  depends  upon  their  electrical  poten- 
tial. This  question  is,  however,  still  an  open  one.  It  was  found 
when  the  air  around  the  magnet  is  rendered  as  quiet  as  possible, 
and  when  no  disruptive  effects  are  permitted  along  the  conductor, 
that  the  magnet  becomes  apparently  stronger.  It  was  also  found 
that  disturbances  of  the  air  around  the  magnet  appeared  to  dimin- 
ish its  deflection  effect.  It  was  found  when  the  charged  magnet 
was  covered  with  tin-foil,  that  the  defection  due  to  electrification 
was  apparently  unchanged.  It  was  found  when  the  air  around  the 
magnet  was  disturbed  by  the  movement  of  an  assistant,  or  by 
means  of  a  palm-leaf  fan,  that  its  deflecting  effect  due  to  electrifi- 
cation was  diminished.  When  the  fan  was  operated  during  alter- 
nate semi-vibrations  of  the  needle,  the  oscillations  of  the  needle 
could  be  gradually  increased  in  amplitude  to  5  or  6°  of  arc. 

All  of  this  evidence  indicates  conclusively,  that  the  apparent 
increase  in  the  strength  of  the  deflecting  magnet  when  in  contact 
with  the  terminal  of  the  machine,  is  due  to  an  increase  in  the 
permeability  of  the  air  around  the  magnet. 

The  " charged"  molecules  of  air  appear  to  behave  like  iron 
filings,  in  that  they  set  in  the  field  of  the  deflecting  magnet  with 
the  planes  of  the  electrical  whirls  at  right  angles  to  the  lines  of 
force.  It  was  found  that  a  solid  steel  magnet  gives  similar  results. 

A  bar  magnet  thus  used  as  a  deflecting  magnet,  over  which 
a  sheet  of  glass  is  placed,  extending  to  the  shield  around  the  needle, 
gives  most  interesting  results  when  the  plate  is  sprinkled  with 
iron  filings.  An  increase  in  the  deflecting  effect  of  the  magnet  is 
thus  produced. 


Variations  in  Permeability  53 

The  increase  in  permeability  due  to  tapping  the  plate  is  plainly 
evident.  When  the  filings  are  gathered  in  a  heap  at  the  equator 
of  the  magnet,  its  deflecting  effect  is  greatly  diminished.  If  at  any 
point  in  the  field  of  this  magnet,  the  iron  filings  are  disturbed  by 
means  of  a  brush,  the  magnetic  field  will  be  disturbed  throughout. 
If  the  iron  filings  were  free  to  move,  they  would  respond  to  the 
disturbance.  The  suspended  needle  does  respond. 

When  the  magnet  is  mounted  on  a  block  resting  upon  the  glass 
plate  and  a  mass  of  iron  filings  is  applied  to  its  ends  only,  the 
deflecting  effect  of  the  magnet  is  increased  in  some  cases  8  or  10 
per  cent.  Disturbance  of  this  mass  of  filings  produces  a  magnetic 
storm,  which  suggests  that  an  aurora  borealis  is  near. 

The  electrified  magnet  was  placed  in  a  glass  tube  having  an 
internal  diameter  of  about  4  cm.  The  tube  extended  to  the  metal 
shield  enclosing  the  needle.  This  metal  shield  was  grounded. 
It  was  then  found  that  the  deflecting  effect  of  the  magnet  was  less, 
than  when  the  magnet  not  connected  with  the  influence  ma- 
chine. When  the  machine  is  stopped,  the  deflection  at  once 
becomes  greater  than  normal,  but  it  quickly  diminishes  to  normal 
value.  The  reason  for  this  was  explained,  by  filling  the  tube  with 
tobacco  smoke  before  the  machine  was  started.  The  column  of 
air  within  the  tube  was  in  continual  commotion  while  the  machine 
was  in  operation.  The  molecules  of  ionized  air  could  not  then  set 
in  orderly  array  along  the  lines  of  force.  It  is  remarkable  that 
under  such  conditions,  the  permeability  of  the  air  column  is  less, 
than  when  the  magnet  is  not  in  communication  with  the  machine. 

When  the  insulated  magnet  was  enclosed  in  a  mass  of  cotton 
batting,  having  a  diameter  of  about  50  cm.,  electrification  of  the 
magnet  had  no  appreciable  effect  upon  its  deflecting  effect.  The 
fibers  of  cotton  then  appear  to  determine  the  lines  along  which 
the  ionized  air-filaments  shall  form. 

While  observing  the  needle  during  a  wind  storm  in  which 
sudden  and  violent  gusts  of  wind  occurred,  it  was  observed  that 
the  vibrations  were  affected  in  a  marked  way  at  the  beginning  of 
a  wind-gust.  The  velocity  of  the  needle  was  suddenly  and  greatly 
changed.  Several  times  it  was  observed  that  when  it  had  come  to 
rest  at  the  extreme  of  a  vibration,  it  would  suddenly  start  into 
motion  and  in  the  direction  in  which  it  had  been  moving.  Some- 
times the  velocity  of  swing  would  be  greatly  diminished,  the  motion 


54  Effect  of  Wind  Gusts 

would  be  arrested  prematurely,  and  in  the  return  swing,  the  veloc- 
ity would  be  increased  to  a  marked  degree.  These  sudden  changes 
in  the  motion  of  the  needle  occurred  at  the  beginning  of  a  gust  of 
wind  of  unusual  severity.  In  one  case  the  unusual  velocity  of 
the  wind  persisted  apparently  unchanged  for  a  couple  of  minutes, 
but  the  change  in  the  motion  of  the  needle  occurred  at  the  begin- 
ning of  the  gust.  The  amplitude  of  successive  semi-vibrations 
would  sometimes  change  from  five  minutes  to  half  a  degree,  or 
the  reverse.  The  amplitude  was  sometimes  observed  to  gradually 
increase  from  zero  to  a  maximum  and  then  diminish  again  to  zero. 
The  maximum  amplitudes  were  greatest  when  the  wind  was  most 
violent  and  when  it  came  in  sudden  gusts.  On  days  when  the 
wind  was  mild  the  maximum  amplitude  would  not  exceed  i°. 
On  days  of  violent  winds  the  amplitude  has  often  risen  to  8  °. 
Notwithstanding  the  fact  that  the  gusts  of  wind  occur  at  irregular 
intervals,  the  variations  in  the  amplitude  of  the  needle  resemble 
an  irregular  series  of  beats.  The  needle  used  in  these  observations 
was  formed  of  steel  rod  about  i  cm.  in  diameter  and  3  cm.  in 
length. 

These  observations  were  made  during  the  spring  of  1913. 
They  were  made  under  conditions  which  made  conclusive  results 
impossible.  Street-cars  600  ft.  distant  produced  disturbances  of 
the  same  order  of  magnitude  as  those  which  were  observed. 

Subsequent  observations  made  at  my  summer  home  at  Hessel, 
Michigan,  showed  that  coincidence  of  a  few  violent  disturbances 
with  a  few  of  the  more  violent  wind-gusts,  was  a  mere  chance  co- 
incidence. Tornadoes  occurred  in  the  surrounding  region  on  two 
days  when  the  disturbances  were  greatest,  and  when  the  winds 
were  most  violent  at  St.  Louis.  In  general  the  results  were  of  a 
character  to  give  weight  to  the  preliminary  conclusion  which  the 
laboratory  experiments  with  the  palm-leaf  fan  had  suggested. 

The  observations  during  the  summer  of  1913  were  made  in  a 
large  tent  18  X-20  feet,  located  about  50  feet  from  the  shore  at 
the  north  end  of  Lake  Huron.  The  cottage  was  about  200  feet 
distant.  The  village  of  Hessel  was  about  half  a  mile  to  the  S.  E. 
Back  from  the  shore  was  pasture  land  and  groves  of  trees. 

The  magnetic  needle  was  a  piece  of  knitting  wire  7  cm.  in 
length,  suspended  upon  a  fiber  of  unspun  silk  about  40  cm.  in 
length.  The  enclosing  case  was  formed  from  a  large  glass  bottle, 


Equipment  of  Magnetic  Station  55 

the  top  of  which  was  removed.  A  metal  cap  fitting  closely 
around  the  top  of  the  glass  jar  thus  formed,  was  provided  with  a 
vertical  brass  tube,  having  at  its  top  a  torsion  head  and  means 
for  attaching  the  suspension  fiber.  This  metal  cap  was  sealed  to 
the  glass  jar  by  means  of  adhesive  rubber  tape.  The  jar  was 
mounted  in  a  closely  fitting  base  provided  with  leveling  screws, 
which  were  about  30  cm.  apart,  in  order  to  secure^  stability.  A 
fine  copper  wire  soldered  to  the  middle  of  the  needle,  served  as 
a  means  for  attaching  the  suspension  fiber.  It  also  extended  be- 
low the  needle,  and  to  its  lower  end  was  attached  a  horizontal  wire 
about  6  cm.  in  length,  which  dipped  into  coal-oil  in  the  bottom  of 
the  jar,  and  served  as  a  damper  for  the  needle.  Attached  to  the 
wire  suspension  of  the  needle  was  a  small  mirror,  by  means  of 
which  the  motion  of  the  needle  was  observed,  in  the  usual  way 
with  a  telescope  and  scale.  The  scale  was  divided  into  centimeters 
and  tenths.  The  scale  value  was  i  mm.  =  3.37  minutes  of  deflec- 
tion of  the  needle. 

The  structure  upon  which  the  needle  and  telescope  were 
mounted,  was  a  frame  constructed  of  2  X  4  inch  timber  bolted 
together  with  brass  bolts,  and  the  legs  or  corner  posts  of  the  frame 
extended  2  feet  down  into  clay  and  gravel  soil.  The  structure 
was  braced  longitudinally  and  transversely,  the  braces  being  held 
in  place  by  large  brass  screws.  The  structure  thus  formed  was 
8  feet  in  length  in  a  north  and  south  direction  with  respect  to 
the  magnetic  meridian,  and  4  feet  in  width. 

The  needle  was  deflected  90°  from  the  magnetic  meridian,  by 
means  of  two  bar  magnets  2  feet  in  length  whose  axes  made  an 
angle  of  45°  with  the  meridian.  The  resultant  field  was  thus  the 
same  as  the  horizontal  component  of  the  earth's  field.  This  re- 
sultant field  was  then  partly  compensated  by  two  bar  magnets  4 
feet  in  length,  on  either  side  of  the  needle,  and  at  the  ends  of  the 
table,  about  4  feet  distant  from  the  needle.  The  final  resultant 
field  in  which  the  needle  was  thus  placed  was  about  0.05  that  of  the 
horizontal  component  of  the  earth's  field.  This  was  determined 
by  the  oscillation  method,  before  the  damping  liquid  was  intro- 
duced. The  time  of  vibration  was  corrected  for  the  torsional 
effect  of  the  suspension  fiber.  This  adjustment  was  not  main- 
tained. Adjustment  of  the  control  magnets  was  occasionally 


56  Equipment  of  Magnetic  Station 

necessary.  The  resultant  field  was  certainly  less  than  the  above 
value  during  some  of  the  work  of  the  summer. 

With  this  arrangement,  the  needle  is  very  sensitive  to  changes 
in  the  horizontal  component  of  the  earth's  field,  and  it  has  the 
advantage  of  permitting  these  changes  to  be  observed  at  any 
instant.  Some  preliminary  observations  were  made  with  the  con- 
trol magnets  exposed  to  the  air.  The  tent  was  provided  with  a 
fly,  which  permitted  a  free  circulation  of  air  between  it  and  the 
roof.  It  however  became  evident  that  the  variation  in  position 
of  the  needle  was  materially  influenced  by  a  variation  in  the  tem- 
perature of  the  magnets,  although  the  maximum  temperature  of 
the  day  during  July  and  August  did  not  exceed  85°  F.  This 
temperature  effect  was  greatly  reduced  by  wrapping  the  magnets 
in  heavy  padded  blankets.  It  was,  however,  soon  eliminated  by 
maintaining  all  of  the  control  magnets  at  a  temperature  of  32°  F. 
This  was  done  by  placing  each  magnet  within  a  piece  of  heavy 
rubber  tubing.  This  tubing  was  of  strong  fiber,  coated  within 
and  without  with  rubber.  The  ends  were  plugged  and  sealed  with 
wax.  The  tubes  with  the  enclosed  magnets  were  mounted  in 
V-shaped  supports  within  boxes  put  together  by  means  of  copper 
nails,  and  calked.  The  boxes  were  then  fillled  with  fragments  of 
ice,  packed  closely  around  the  rubber  tubes.  The  ends  of  the 
boxes  rested  on  the  side  timbers  of  the  frame  so  that  the  blankets 
could  be  wrapped  around  the  boxes.  The  boxes  were  provided 
with  outflow  tubes  of  brass. 

The  maintaining  of  the  control  magnets  at  a  fixed  temperature, 
diminished  the  daily  swing  of  the  magnetic  needle  in  a  very 
appreciable  degree.  It  did  not  apparently  affect  the  character  of 
the  changes  due  to  wind-gusts  and  cloud  shadows.  It  did,  how- 
ever, serve  to  remove  all  possible  doubt  from  the  conclusions.  In 
this  series  of  observations,  it  was  not  the  object  to  make  precise 
measurements  of  the  quantities  involved.  It  was  a  search  for 
fundamental  phenomena.  For  precise  measurements  the  two 
sets  of  magnets  might  each  be  replaced  by  two  coils  as  in  the 
Helmholtz-Gaugain  galvanometer.  These  might  be  mounted  on 
a  table  capable  of  rotating  around  a  vertical  axis  coincident  with 
the  suspension  fiber.  Two  telescopes  with  scale  mounted  90° 
apart  upon  the  table  would  serve  to  properly  adjust  the  table 
when  both  circuits  were  open,  and  to  deflect  the  needle  90°.  The 


Magnetic  Storm  Due  to  Wind  57 

current  in  the  deflecting  coils  would  be  increased  until  the  tele- 
scope with  axis  east  and  west  is  directed  upon  the  reading  cor- 
responding to  the  magnetic  axis  of  the  needle,  as  determined  by 
the  other  telescope,  the  torsion  head  being  turned  90°. 

The  current  and  the  constant  of  the  coils  being  known,  the 
value  of  H  is  determined  at  that  instant.  The  resultant  field 
could  then  be  decreased  to  any  desired  amount  by  closing  the 
circuit  containing  the  compensating  coils,  and  varying  the  current 
by  means  of  a  proper  resistance  (carbon  plates  with  a  compression 
screw) . 

It  was  of  course  found  that  in  general  the  intensity  H  of  the 
horizontal  component  of  the  earth's  field,  increases  during  the 
day,  reaching  a  maximum  late  in  the  afternoon.  The  numerical 
value  of  H  is,  however,  greater  on  clear  days  than  on  cloudy  days. 
On  days  which  are  clear  in  the  forenoon  and  cloudy  in  the  after- 
noon, the  maximum  may  occur  in  the  middle  of  the  day,  or  before 
noon.  During  days  when  the  air  is  quiet,  the  needle  is  more  quiet 
during  cloudy  or  clear  days,  than  when  the  sky  is  covered  with 
small  clouds  with  blue  sky  between. 

On  days  when  the  wind  blows  in  gusts  at  intervals  of  i  or 
2  minutes  the  needle  is  more  unsteady  in  its  movements  than 
on  quiet  days,  or  on  days  when  the  wind  is  more  uniform. 

On  days  when  gusts  of  wind  are  frequent,  it  is  impossible  to 
identify  any  particular  wind-gust  with  any  particular  disturbance 
of  the  needle.  The  reason  for  this  appears  to  be  explained  by  an 
observation  made  on  July  14.  During  the  forenoon  of  that  day 
the  wind  was  very  mild  from  the  west.  Shortly  before  i  o'clock 
the  wind  suddenly  changed  to  the  south,  while  it  continued  at 
the  rate  of  3  to  4  miles  per  hour.  At  i  :  10  p.m.  the  needle  began 
to  vibrate  to  and  fro.  The  scale  reading  at  each  extreme  position 
was  recorded.  This  was  continued  for  9  minutes,  when  a  blast 
of  wind  came  in  from  the  lake  to  the  south.  It  overturned  a  sail 
boat  lying  at  a  dock  about  200  feet  distant,  the  sails  of  which  had 
been  raised  in  order  to  dry  them.  It  was  by  far  the  most  violent 
wind  of  the  summer.  About  8  minutes  later  the  wind  had 
practically  ceased,  and  the  vibrations  of  the  needle  had  also  ceased. 
The  scale  reading  had  been  under  constant  observation  before 
the  gust  of  wind  began.  The  reading  was  recorded  each  minute, 
and  even  more  frequently  during  times  of  mild  disturbance,  when 


58  Magnetic  Storm  Due  to  Wind 

slow  to  and  fro  movements  made  this  necessary.  When  the 
movement  was  apparently  uniform  in  one  direction,  records  were 
made  at  intervals  of  5  or  10  minutes,  although  the  needle  was 
under  almost  constant  observation.  Readings  were  always  made 
when  the  direction  of  motion  was  reversed. 

During  the  oscillations  above  referred  to,  the  watch  reading 
was  taken  at  as  frequent  intervals  as  was  possible.  In  these 
oscillations  the  time  of  one  to-and-fro  vibration  was  about  50 
seconds,  as  nearly  as  it  could  be  determined.  The  time  covered  by 
consecutive  vibrations  frequently  varied  so  greatly  on  other 
occasions  that  no  precise  value  could  be  given  for  the  time  of 
vibration.  The  effect  of  the  damping  liquid  was  such  that  the 
needle  would  come  practically  to  rest  in  three  or  four  semi- vibra- 
tions when  deflected  90°. 

These  vibrations  above  described  are  graphically  shown  in 
Plate  VI.  The  instant  when  the  blast  of  wind  reached  the  observ- 
ing station  is  indicated  by  the  arrow,  located  near  the  middle  of  the 
group  of  vibrations  representing  this  local  magnetic  storm.  The 
ordinates  are  in  scale  divisions.  The  greatest  amplitude  of  swing 
was  about  20  scale  divisions.  The  hour  of  the  day  is  laid  off  upon 
the  horizontal  axis.  The  fact  that  the  needle  was  affected  by  this 
air  disturbance  south  of  the  station  at  least  9  minutes  before 
it  reached  the  station,  is  in  exact  harmony  with  the  suggestion 
given  in  a  paper  in  the  Transactions  of  the  Academy  of  Science  of 
St.  Louis  and  above  discussed.  As  was  there  pointed  out,  a  brush 
which  disturbs  iron  filings  at  any  point  on  a  plate  of  glass  above 
a  bar  magnet,  is  producing  an  ether  disturbance  in  the  field  of 
that  magnet.  This  observation  also  shows  clearly,  why  it  is  that 
on  stormy  days,  when  gusts  of  wind  follow  each  other  at  frequent 
intervals,  the  effect  due  to  any  gust  cannot  be  identified.  At  any 
instant,  the  needle  responds  to  a  summation  of  these  disturbances. 
An  inspection  of  Plate  VI  will  show  that  the  disturbing  effect  of 
this  gust  of  wind  probably  began  at  about  12  :  55,  or  about  24  min- 
utes before  it  reached  the  station.  This  was  the  time  when  the 
wind  changed  in  direction. 

It  could  hardly  be  expected  that  such  a  wind  disturbance  could 
produce  a  magnetic  storm  of  more  than  a  local  character.  But 
it  is  not  at  all  improbable  that  tornadoes  and  tropical  cyclones 
may  produce  much  more  widespread  effects.  A  wind  disturbance 


Auroral  Disturbances  59 

among  the  atmospheric  ions  which  accumulate  along  the  magnetic 
lines  of  force  at  or  near  the  earth's  magnetic  poles,  might  be  ex- 
pected to  produce  the  effects  which  have  long  been  observed. 

We  need  not  consider  the  source  or  origin  of  this  electrification 
at  the  magnetic  poles  of  the  earth.  It  is  enough  for  us  to  know 
that  it  exists.  Its  effect  upon  the  magnetic  field  of  the  earth  is 
similar  to  that  produced  by  masses  of  iron  filings,  applied  to  the 
ends  of  a  bar  magnet,  on  the  field  of  that  magnet. 

A  wind  disturbance  here  would  produce  a  magnetic  storm  over 
a  vastly  greater  area  than  would  a  similar  wind  storm  in  lower 
latitudes.  A  wind-storm  progressing  in  an  easterly  direction 
around  and  near  one  of  the  magnetic  poles  of  the  earth  might  pro- 
duce progressive  easterly  disturbances  in  lower  latitudes  such  as 
have  been  discussed  by  Bauer.  The  velocity  of  progression  of 
such  a  magnetic  storm  as  observed  in  lower  latitudes,  would 
depend  upon  the  nearness  of  the  wind  disturbance  to  the  magnetic 
pole. 

On  ten  or  twelve  occasions  magnetic  storms  were  observed, 
which  were  caused  by  a  local  dash  of  rain.  When  rain  falls  con- 
tinuously or  at  intervals  during  a  day  when  the  sky  is  covered  with 
clouds,  which  extend  over  adjoining  states,  the  needle  shows  no 
appreciable  disturbance.  The  horizontal  component  of  the  earth's 
field  is  then  much  weaker  than  it  would  be  if  the  sky  were  clear, 
but  there  is  no  additional  change  due  to  a  rainfall.  The  limiting 
condition  has  been  already  reached. 

When  small  clouds  are  scattered  over  the  sky  and  a  local  fall 
of  rain  occurs  at  the  observing  station,  the  sunlight  passing  through 
the  air  through  which  the  rain-drops  fall,  a  very  marked  magnetic 
storm  is  produced.  Such  a  disturbance  is  represented  in  Plate 
VII. 

This  rain,  which  was  very  violent,  began  while  I  was  at  the 
noon-day  meal.  It  lasted  about  10  minutes.  When  the  tent 
was  reached  the  rain  had  practically  ceased  at  the  station.  The 
sun  was  visible  during  most  of  the  time  while  the  rain  was  falling. 
The  area  covered  by  the  rain  was  probably  not  over  i  or  2 
square  miles.  Its  boundary  could  be  seen  upon  the  lake  to  the 
south,  while  I  was  on  the  way  to  the  tent.  The  needle  showed  that 
we  were  then  in  the  midst  of  one  of  the  most  violent  magnetic 
storms  of  the  summer.  The  vibrations  ceased  about  5  minutes 

5 


60  Magnetic  Storm  Due  to  Rain 

after  observation  began.  The  extreme  reading  of  the  scale  for 
each  oscillation  was  taken.  They  are  represented  in  Plate  VII, 
together  with  subsequent  readings  of  the  needle  represented  on  the 
same  time  scale.  Readings  made  before  leaving  the  tent  for  lunch 
are  also  shown.  The  gap  between  the  readings  before  and  after 
lunch  is  only  in  part  represented,  as  is  indicated  by  the  figures  at 
the  bottom  of  the  plate  representing  the  hour  of  the  day.  The 
needle  was  in  a  more  disturbed  condition  after  the  vibrations  had 
ceased  than  it  had  been  before.  Evidently  the  rain  had  some  effect 
upon  the  magnetic  field  at  the  station,  when  it  was  falling  through 
air  to  the  south  of  the  station,  and  had  ceased  at  the  station. 
The  needle  was  damped  during  this  day,  so  that  summation  effects 
were  impossible,  nevertheless  in  one  of  these  oscillations  the  needle 
vibrated  through  an  arc  of  over  5°. 

This  rain  occurred  on  August  26.  A  diagram  representing 
the  movement  of  the  needle  between  10  a.m.  and  sunset  on  that 
day,  is  represented  in  Plate  VIII.  The  vibrations  due  to  the  rain 
occurred  at  the  close  of  the  first  gap  in  that  curve.  They  cannot 
be  properly  represented  here  with  the  time-scale  used  in  this  plate. 
They  are  replaced  by  a  straight  line.  The  second  gap  in  the  dia- 
gram represents  the  time  required  to  finish  the  noon-day  meal, 
which  had  been  interrupted  by  the  rain.  The  part  of  the  diagram 
of  Plate  VII,  after  the  hour  of  i :  05,  is  the  part  which  in  Plate  VIII 
lies  between  the  two  gaps. 

Plate  VIII  also  represents  the  effect  upon  the  horizontal  com- 
ponent of  the  earth's  field,  of  two  large  dense  and  sharply  defined 
clouds  passing  over  the  sun.  Their  effect  is  shown  at  points  cor- 
responding to  ii  :io  a.m.  and  4: 28  p.m.  During  seven  weeks  the 
needle  had  been  under  constant  observation,  from  sunrise  to  sun- 
set, in  order  to  secure  the  results  which  were  here  obtained.  On 
many  days  evidence  of  cloud  effects  were  observed  which  seemed 
conclusive,  but  usually  the  edges  of  the  cloud  would  not  be  sharply 
defined.  In  some  cases  the  edges  would  be  more  or  less  transpar- 
ent, in  some  cases  small  clouds  of  irregular  form  would  surround 
the  larger  cloud.  It  often  happened  that  large  dense  clouds  ap- 
peared to  be  approaching  the  sun,  and  the  needle  gave  results 
which  were  wholly  different  from  those  which  had  been  expected. 
On  going  out  of  the  tent  it  would  be  found  that  the  cloud  had 
behaved  in  a  wholly  different  manner  from  what  had  been  expected. 


Magnetic  Effect  of  Cloud  Shadows  61 

In  some  cases  it  practically  disappeared  before  it  reached  the  sun. 
Sometimes  it  was  dispersed  into  smaller  clouds,  which  were  more 
or  less  hazy  in  outline.  Their  effect  was  often  appreciable  and 
persuasive,  and  yet  more  or  less  unsatisfactory. 

The  fact  that  it  was  impossible  to  predict  at  what  moment  the 
desired  conditions  might  present  themselves,  and  the  necessity 
for  having  a  record  of  the  behavior  of  the  needle  for  a  considerable 
time  interval  before  the  sun  entered  a  dense  cloud,  made  it  neces- 
sary to  keep  the  needle  and  the  clouds  under  constant  observation, 
recording  the  results  during  each  minute  of  the  day,  sometimes  at 
lesser  intervals,  so  far  as  this  was  possible.  The  only  interrup- 
tion to  this  work  during  July  and  August  was  from  August  12 
to  1 6,  during  which  interval  a  severe  attack  of  a  painful  illness 
made  work  of  any  kind  impossible. 

The  sun  entered  the  well-defined  edge  of  the  first  cloud  above 
referred  to  at  10  :  45  a.m.  The  needle  had  been  previously  moving 
continuously  in  a  direction  such  as  would  be  caused  by  a  steady 
increase  in  the  strength  of  the  field.  When  the  sun  entered  the 
cloud,  irregularities  in  the  movement  of  the  needle  were  observed. 
The  air  on  the  border  of  a  cloud  shadow  often  gave  evidence  of  a 
disturbed  condition.  In  this  case  the  sun  was  in  the  center  of  the 
cloud  at  about  11:01.  This  cloud  then  covered  the  overhead  sky 
down  to  about  45°  from  the  horizon.  Below  this  cloud  the  sky 
was  clear.  The  sun  reappeared  at  n  h.  12  m.  30  sec.  At  this 
time  the  scale  reading  corresponded  to  the  minimum  shown  in  the 
diagram,  Plate  VIII.  The  needle  at  once  reversed  its  direction 
of  movement.  The  reading  at  1 1 : 40  or  11:50  was,  as  the  diagram 
shows,  about  what  it  would  have  been  if  the  cloud  had  not 
appeared. 

This  cloud  was  soon  afterward  broken  up  into  smaller  clouds, 
and  other  smaller  clouds  appeared.  From  12 : 30  to  2  p.m.  the  sky 
was  partly  covered  here  and  there  by  smaller  clouds,  so  that  at  the 
station,  as  at  surrounding  points,  the  sun  was  visible  at  and  during 
frequent  intervals.  One  of  these  small  clouds  unexpectedly  gave 
rise  to  the  dash  of  rain  before  discussed.  The  general  effect  of 
these  clouds  is  shown  in  the  general  drop  in  the  curve  between 
12:30  and  1:30  p.m. 

The  sun  entered  another  dense  and  sharply  defined  cloud 
surrounded  by  clear  sky,  at  4  : 20  p.m.  of  this  same  day,  after  the 


62  Magnetic  Storms  and  Weather 

daily  maximum  had  been  passed.  It  emerged  from  this  cloud 
at  4 :  28  p.m.  While  the  sun  was  hidden  by  this  cloud,  the  intensity 
of  the  magnetic  field  diminished  as  in  the  other  case,  as  is  shown  by 
the  drop  in  the  curve.  When  the  sun  reappeared  the  intensity  at 
once  began  to  increase.  At  4: 37  the  reading  was  that  correspond- 
ing to  the  general  trend  of  the  curve  during  that  afternoon.  The 
time  of  entering  and  leaving  the  cloud  is  in  both  cases  indicated  on 
the  diagram  by  arrows. 

It  would  thus  appear  that  cloud  shadows  during  the  day  have 
the  same  effect  upon  the  earth's  magnetic  field  that  the  earth's 
shadow  has  at  night.  The  lines  of  the  field  sway  around  them. 
They  sway  above  the  clouds  into  the  sunlight.  The  horizontal 
component  would  thus  be  diminished  below  the  clouds. 

It  is  impossible  to  present  here  the  full  evidence  obtained, 
which  to  me  seems  to  establish  beyond  all  question  the  conclusion 
that  local  variations  in  the  earth's  magnetic  field  are  determined 
wholly  by  local  weather  conditions.  It  is  contained  in  300  pages 
of  closely  written  notes  on  pages  8  inches  square.  While  it  might 
at  first  seem  that  the  greater  part  of  this  record  was  of  no  impor- 
tance, it  does  establish  the  general  conclusion  that  when  local 
conditions  were  uniform,  whatever  they  might  be,  the  magnetic 
needle  showed  no  marked  disturbance  of  an  abrupt  character, 
such  as  we  have  in  these  vibrations. 

It  may  suffice  to  discuss  briefly  the  record  of  July  19.  In 
doing  this  the  weather  maps  kindly  furnished  by  the  Weather 
Bureau  at  Washington  were  of  material  assistance.  On  the  after- 
noon of  this  day,  the  needle  showed  more  disturbance  than  on  any 
other  day.  At  10  a.m.  a  rain  cloud  was  observed  in  the  southern 
horizon.  At  11:45  the  needle  began  to  vibrate,  the  average 
amplitude  of  vibration  being  about  20  scale  divisions,  and  some- 
times reaching  35.  The  wind,  which  had  been  from  the  north- 
west, had  changed  to  the  south.  This  continued  until  about  12:10 
p.m.,  when  the  needle  became  less  disturbed,  and  observations 
ceased  until  12 :45  p.m.  During  this  disturbance,  it  could  be  seen 
that  a  rain  was  falling  on  the  lake  to  the  south.  At  1 2 : 45  a  violent 
dash  of  rain  began,  which  continued  for  10  minutes,  and  then 
continued  as  a  milder  rain  until  1:05.  The  clouds  were  not  con- 
tinuous over  the  sky.  The  sun  appeared  at  intervals. 

The  point  of  importance  is  that  these  vibrations  began  and 


Magnetic  Storms  and  Weather  63 

continued  for  an  hour,  while  a  rainstorm  existed  to  the  south  of 
the  station.  During  the  remainder  of  the  afternoon  periods  of 
sunshine  and  rain  came  in  alternation.  Between  2:37  and  3  : 10 
over  half  an  inch  of  rain  fell,  from  what  appeared  to  be  a  local 
cloud.  The  needle  continued  to  vibrate  during  this  rain,  and 
after  it  had  ceased  at  the  station  and  while  its  roar  could  be  heard 
upon  the  lake  to  the  south.  The  wind  was  very  mild  during  the 
entire  day,  its  velocity  not  at  any  time  exceeding  8  or  10  miles  per 
hour.  The  amplitude  of  the  vibrations  sometimes  reached  40 
scale  divisions.  The  greatest  amplitude  of  the  day  was  49  scale 
divisions.  The  needle  was  damped  during  this  day. 

The  data  given  on  the  weather  map  show  that  the  rain  which 
visited  the  observing  station  extended  from  Escambia,  which  is  in 
northern  Michigan,  near  the  north  end  of  Lake  Michigan,  to 
Alpena,  which  is  in  southern  Michigan,  near  the  north  end  of 
Lake  Huron.  At  the  former  station  the  rainfall  was  0.44  inch  and 
at  the  latter  it  was  0.36  inch.  At  Saginaw,  Mich.,  which  is  south 
of  Alpena  and  also  on  the  west  side  of  Lake  Huron,  the  rainfall  was 
0.26  inch.  At  Sault  Ste.  Marie,  at  the  outlet  of  Lake  Superior, 
no  rain  fell.  This  rainstorm  was  a  purely  local  one,  extending 
across  the  head  of  Lake  Michigan  and  along  the  straits  of  Macki- 
nac,  and  probably  into  Lake  Huron. 

On  July  1 6,  26,  27  and  31  similar  local  rains  occurred  in  the 
same  region  during  the  midday  hours.  In  some  cases  there  was 
practically  no  rainfall  at  Hessel,  but  the  clouds  which  were  ob- 
served near  the  horizon  were  recognized  as  rain  clouds.  The 
weather  maps  show  that  rain  fell  at  surrounding  weather  stations. 
On  all  of  these  days,  the  needle  was  in  to-and-fro  vibration  at 
intervals  during  the  day.  In  all  cases  when  the  weather  maps 
show  rains  in  this  region,  which  occurred  during  the  hours  of 
observation  of  the  needle,  the  needle  showed  such  vibrations. 

On  three  days  they  were  observed  when  violent  gusts  of  wind 
occurred  at  the  station,  with  no  rain  in  that  part  of  the  country. 

On  August  23,  very  marked  and  sudden  changes  in  the  position 
of  the  needle  were  observed,  and  they  were  so  unusual  as  to  lead 
to  the  suspicion  that  something  unusual  must  have  happened. 
There  were  no  vibrations  accompanying  those  disturbances.  The 
day  was  unusually  clear.  Very  light  rains  occurred  at  all  of  the 
nearest  weather  stations,  the  greatest  fall,  0.20  inch,  being  at 


64  The  Sunset  Storm 

Houghton,  about  200  miles  distant  in  a  direction  a  little  north  of 
west. 

On  August  8,  a  violent  rain  accompanied  by  a  continuous  roar 
of  overhead  thunder  occurred  between  4  and  6  130  a.m.  The 
needle  was  then  very  quiet,  as  was  the  case  on  every  morning  of 
the  summer  with  one  exception.  On  this  morning  when  a  few 
oscillations  occurred  after  sunrise,  they  were  accompanied  by 
violent  gusts  of  wind. 

On  two  or  three  occasions  results  were  observed  which  sug- 
gested that  winds  from  the  north,  reaching  the  station  through  a 
grove  of  trees,  had  a  slightly  different  effect  from  that  of  a  wind 
from  the  lake.  This  subject  requires  additional  attention. 

Perhaps  the  most  interesting  phenomenon  observed  during  the 
summer  was  the  continuous  vibration  of  the  needle  during  a  period 
varying  from  half  an  hour  to  two  hours  preceding  sunset.  This 
was  observed  on  nearly  every  evening  when  the  western  sky  was 
clear.  The  vibrations  were  greatest  when  the  day  had  been  clear, 
and  the  intensity  of  the  field  had  reached  a  high  maximum.  They 
did  not  occur  when  the  afternoon  sky  was  covered  with  a  dense 
cloud.  The  cloud  shadow  is  then  joined  to  the  earth's  shadow. 
They  did  not  occur  in  the  morning,  either  before  or  after  sunrise. 
Observations  were  sometimes  begun  as  early  as  2  o'clock  a.m. 
They  were  usually  begun  about  an  hour  before  sunrise. 

Plate  IX,  made  from  observations  on  August  31,  gives  an 
illustration  of  these  sunset  disturbances.  The  plate  shows  how 
the  needle  moved  during  the  afternoon,  before  the  oscillations 
suddenly  began.  In  the  original  drawing,  this  part  of  the  curve 
was  drawn  to  a  time  scale  of  6  cm.  per  hour.  For  the  period 
during  which  the  oscillations  are  represented,  the  time  scale  is 
6  cm.  to  about  3  minutes.  One  to-and-fro  oscillation  was  drawn 
to  each  half-centimeter.  During  this  day  the  damping  liquid 
had  been  removed.  It  will  be  observed  that  the  disturbing  cause 
ceased  at  about  5  : 45  and  the  needle  gradually  came  to  rest.  On 
this  day  two  similar  violent  disturbances  occurred  subsequently 
before  sunset,  which  are  not  represented  in  Plate  IX.  The  greatest 
amplitude  reached  was  about  250  scale  divisions,  or  about  14°  of 
arc.  The  extreme  scale  reading  for  each  and  every  vibration  was 
read. 

In  nearly  all  of  the  observations  on  this  sunset  disturbance, 


Wireless  Telegraphing  and  Magnetic  Storms  65 

the  motion  of  the  needle  was  restrained  by  the  damping  fluid. 
The  amplitude  of  the  vibrations  was  then  in  general  over  an 
angle  not  exceeding  50  scale  divisions  or  2.8  degrees.  The  time 
of  vibration  was  practically  the  same  whether  the  damping  fluid 
was  used  or  not.  It  was  not  uniform  in  either  case.  The  vibra- 
tion of  the  damped  needle  frequently  continued  without  cessation 
for  an  hour  or  more.  At  this  hour  of  the  evening  there  was  usually 
no  wind  at  the  station. 

It  is  evident  that  along  what  may  be  called  the  sunset  meridian, 
there  will  generally  be  places  where  cloud  shadows  are  joined  to 
the  earth's  shadow.  Since  only  the  horizontal  component  of  the 
earth's  field  of  force  is  effective  in  action  upon  the  needle,  we  may 
consider  the  conditions  which  would  exist  in  a  field  of  force  in  which 
the  lines  are  horizontal.  Where  the  clouds  occur,  these  lines  tend 
to  sway  above  the  clouds  into  the  sunlight.  If  we  consider  these 
lines  to  behave  like  elastic  threads,  they  are  elongated  by  this 
distortion.  They  snap  asunder  and  disappear  as  they  are  thus 
distorted  and  forced  toward  the  approaching  shadow  of  the  earth, 
the  field  diminishing  in  strength  in  a  rhythmical  way.  This  state- 
ment must  be  considered  as  figurative  in  character,  but  it  is  in  a 
certain  sense  descriptive  of  the  observed  phenomena.  It  is  with 
some  surprise  that  I  find  that  this  sunset  disturbance  has  not 
been  observed  at  stations  where  continuous  records  are  made. 
This  conclusion  obtained  from  an  examination  recently  made  of 
government  publications  has  been  confirmed  by  information  just 
received  from  the  Chief  of  the  U.  S.  Coast  and  Geodetic 
Survey.  Evidently  the  subject  deserves  additional  attention. 
It  is  evident  that  this  is  the  high  sea  with  which  wireless  messages 
are  contending  in  what  is  called  the  sunset  effect. 

It  is  also  evident  that  local  changes  in  magnetic  permeability 
are  the  causes  of  local  magnetic  storms.  Local  rains,  wind-gusts 
and  cloud  shadows  in  air  which  has  been  ionized  by  solar  radia- 
tion bring  about  what  is  called  the  day  effect  in  wireless  telegraph- 
ing. It  has  long  been  known  that  a  public  speaker  can  be  heard 
most  distinctly,  when  other  sources  of  sound  waves  are  not  simul- 
taneously active  in  the  audience  which  he  addresses. 

It  will  of  course  be  understood  that  the  fact  that  wind-gusts 
a  few  miles  distant  are  found  to  affect  a  magnetic  needle,  is  in 


66  Early  History 

harmony  with  the  well-known  fact  that  solar  disturbances  also 
affect  it. 

The  observation  of  Young  at  Sherman,  Idaho,  on  August  3, 
1872,  showed  that  a  solar  outburst  produces  electro-magnetic 
waves,  which  travel  with  the  velocity  of  light.1  The  effect  on  the 
magnetic  needle  at  Greenwich  and  Stony  hurst  was  recorded  at  the 
same  instant,  that  a  solar  disturbance  was  observed  by  Young 
(within  the  instrumental  errors).  Such  results  should  lead  us  to 
expect  that  wind-gusts  in  air  ionized  by  sunlight  or  by  solar  dust, 
as  has  been  pointed  out  by  Arrhenius,  should  produce  similar 
results  of  a  more  local  character. 

In  1823,  Barlow2  made  an  experimental  study  of  the  diurnal 
variation  of  the  earth's  magnetic  field.  He  deflected  the  needle 
into  an  east  and  west  position,  by  means  of  two  control  magnets, 
lying  in  the  magnetic  meridian,  acting  upon  opposite  ends  of  the 
needle.  At  his  request,  his  associate,  Christie,  continued  the 
work.  The  effect  of  the  earth's  field  was  in  part  compensated 
by  a  magnet  parallel  to  the  dip  needle.  Their  papers  are  in 
sequence  in  the  Phil.  Trans,  of  the  Royal  Society  for  1823.  Barlow 
gives  his  conclusion  as  follows: 

"It  appears  to  me  that  the  quantity  of  daily  change  depends 
in  a  greater  degree  on  the  intensity  of  the  solar  light,  than  on  the 
mere  temperature  of  the  day,  although  it  is  certain  from  some  re- 
cent experiments  of  Mr.  Christie,  that  the  change  of  temperature 
of  the  air  during  the  day,  has  a  much  greater  effect  upon  the 
intensity  of  the  opposing  magnets  than  I  could  possibly  have 
imagined." 

Christie  varied  the  temperature  of  the  control  magnets  by 
placing  upon  them  paper  moistened  with  cold  and  with  hot  water. 
He  concluded  from  the  effect  thus  produced  upon  the  magnets, 
that  temperature,  if  not  the  only  cause,  is  the  principal  cause  of 
the  daily  variation  in  the  earth's  field. 

A  part  of  the  work  of  both  Barlow  and  Christie  was  done  in 
their  gardens,  and  the  remainder  in  their  houses,  which  were 
about  a  mile  apart.  Both  found  great  differences  in  the  daily 

1  The  Sun.     By  Young,  p.  158. 

2  Barlow  should  not  be  forgotten.     He  was  the  first  to  make  an  electric  motor. 
Barlow's  wheel  is  the  rotating  armature  of  an  electric  motor.     Eight  years  later 
Faraday  reversed  this  toy   motor,   and  produced   the   first  electrical  generator. 
Neither  of  these  men  realized  what  he  had  accomplished. 


Early  History  67 

variation  indoors  and  in  open  air,  and  various  possible  causes  for 
it  are  discussed.  Barlow  concludes  that  it  is  probably  due  to  the 
cause  discovered  by  Christie,  although  well  known  before  his  time, 
that  the  intensity  at  any  point  in  the  field  of  a  bar  magnet  depends 
upon  the  temperature  of  that  magnet.  He  ascribes  this  difference 
to  the  different  temperature  conditions  of  the  control  magnets. 
Nevertheless  he  is  of  the  opinion  that  the  quantity  of  daily  change 
in  the  earth's  field  depends  in  a  greater  degree  upon  the  intensity 
of  solar  light,  than  upon  the  mere  temperature  of  the  day.  Evi- 
dently his  intuitive  faculty  was  of  a  high  order. 

Barlow's  conclusion  did  not  carry  with  it  any  rational 
explanation  of  causes,  since  at  that  time  ionization  of  the  air,  by 
sunlight,  resulting  in  an  increase  of  its  permeability,  was  unknown. 
The  work  of  Christie  also  raised  a  doubt  in  the  minds  of  others. 
Subsequent  writers  seem  to  have  found  it  necessary  to  say  that 
the  daily  variation  and  local  magnetic  storms  had  not  been  satis- 
factorily explained. 

On  January  27,  1831,  Barlow  presented  a  paper  to  the  Royal 
Society.  In  this  paper  he  refers  to  the  discoveries  of  Oersted, 
Ampere  and  Seebeck.  He  refers  to  the  work  of  Seebeck  as  another 
link  in  the  chain  of  evidence,  that  "  terrestrial  magnetism  is  purely 
an  electrical  phenomenon,  deriving  its  origin  during  the  diurnal 
revolution  of  the  earth  from  the  action  of  the  sun's  rays  in  succes- 
sive portions  of  its  surface,  in  directions  parallel  to  the  equator." 

He  describes  in  this  paper,  a  model  illustrative  of  his  ideas  at 
that  time.  It  was  a  sphere  of  wood  in  which  were  laid  conducting 
wires,  lying  in  grooves  along  parallels  of  latitude.  Electric  cur- 
rents in  these  wires  produced  around  the  sphere  a  magnetic  field 
like  that  of  the  earth. 

During  the  last  fifteen  years  the  present  writer  has  made 
various  attempts  to  produce  a  local  magnetic  storm  in  the  earth's 
field  by  means  of  small  amounts  of  high  power  explosives.  The 
results  discussed  in  the  present  paper  seem  to  indicate  beyond 
question  that  such  explosions  are  capable  of  producing  magnetic 
disturbances.  The  effect  of  the  gust  of  wind  shown  in  Plate  VI 
was  to  produce  an  ether  disturbance  extending  far  beyond  and  in 
advance  of  any  air  waves,  or  air  disturbance. 

Recent  experiments  with  dynamite  on  the  grounds  adjoining 
the  buildings  of  Washington  University  have  not  given  conclusive 


68  Early  History 

results.  It  is  difficult  to  eliminate  other  disturbances,  and  it  is 
not  permissible  to  use  as  large  a  quantity  of  the  explosive  as  will 
probably  be  necessary.  It  is  hoped  that  this  work  may  be  contin- 
ued at  Hessel  during  the  summer  of  1914.  It  seems  probable 
that  a  disturbance  of  this  kind,  originating  in  ionized  air,  should 
be  capable  of  producing  an  effect  on  the  receiving  apparatus  of 
a  wireless  station. 

As  this  volume  is  about  to  be  published,  I  learn  through  the 
courtesy  of  the  Chief  of  the  U.  S.  Coast  and  Geodetic  Survey, 
that  Bauer  has  announced  that  the  local  effect  of  the  moon's 
shadow  during  a  solar  eclipse,  upon  the  magnetic  field  of  the  earth, 
was  similar  to  that  of  the  earth's  shadow  at  night.  The  correct- 
ness of  this  conclusion  is  beyond  all  doubt.  Nevertheless  this 
work  should  be  repeated  during  future  eclipses,  with  more  sensitive 
instruments  than  have  been  heretofore  used.  It  seems  evident 
that  we  can  now  explain  the  causes  not  only  of  local  magnetic 
storms,  but  also  the  causes  of  the  daily  and  annual  variation  of  the 
magnetic  field  of  the  earth. 


69 


T 


1- 


±1 


PLATE  VI. — MAGNETIC  STORM  DUE  TO  WIND. 


PLATE  VII. — MAGNETIC  STORM  DUE  TO  RAIN. 


71 


PLATE  VIII. — EPPECT  OF  CLOUD  SHADOWS. 


PLATE  IX. — MAGNETIC  STORM  AT  SUNSET. 


INDEX 


After-effects,  40,  41 
Arc  discharge,  26 
Attraction  between  masses,  19 
Aurora  borealis,  59 

Ball-lighting  effects,  35-37 

Barlow,  work  of,  66,  67 

Bauer,  effect  of  moon's  shadow,  68 

progressive  magnetic  storms,  59 
Becquerel,  Edmund,  on  buckling  of  wires, 
48 

Canal  rays,  5,  6,  7,  10 

Christie  on  temperature  effects,  66 

Cloud  shadows,   their  magnetic  effect, 

60-62 

Conduction  in  gases,  13,  14,  25,  26 
Critical  spark  length,  26 
Crookes  dark-space,  24 

Dark  and  luminous  columns  in  multiple, 

24-26 

discharge,  3,  6 

De  Nelis,  on  electrical  explosion,  20 
Disruptive    discharge,    conditions    for, 

n,  12,  15 

effect  of  paper  in  preventing,  10 
effect  of  metal  sheet  in  preventing, 

ii 

path  of,  10-14 
Drainage  column,  9,  10,  24 
lines,  14,  15 
steamers,  7,  8 

Early  history,  66-68 
Electrical  convection,  26,  38 
Evaporation  of  electrified  water,  50 
Explosive  condition  of  matter,  19-23 

Faraday  dark-space,  24,  25 
Fatigue  effects,  40,  41 

Hittorf  tube,  26 

High  potential  lines,  27-34 

Inflow  of  negative  corpuscles,  32-34 

Lighting  discharges,  16,  17 
Local  variations  and  local  weather,  62, 
65 

Magnetic   disturbance    due    to   clouds, 

60-62 

station,  equipment  of,  54-56 
storm,  artificial,  52,  53 


Magnetic  disturbance,  due  to  rain,  60 

due  to  wind,  58,  59 

at  sunset,  64,  65 
storms  and  weather,  62,  63 
Maxwell  on  velocity  of  electricity,  41 

Negative  glow,  2,  5,  24 

Newton's  law  for  attraction,  19,  20 

Oscillations,  electrical,  5,  6,  47 

Palm-leaf  fan,  magnetic  storm  produced 
by,  52 

Paper     strip     obstructs     the     positive 

column,  10 
prevents  passage  of  spark,  10 

Pendulum,  the  electrical,  i 

Permeability  and  atmospheric  disturb- 
ance, 53 

Positive  column,  5,  10,  12,  18 

Pumping  service,  electrical,  42-44 

Rain,  magnetic  storm  due  to,  59,  62 
Rowland  effect,  the,  38 
reversed,  39 

Shadow  images,  40,  41 

of  the  moon  in  eclipses,  magnetic 

effect  of,  68 

Shadows  in  the  positive  column,  9 
Shield  of  metal  in  the  positive  column, 

2,  3,  5,  6,  ii 

Singer  on  electrical  explosion,  20 
Solar  outbursts  and  magnetic  storm,  66 
Steam,  decomposition  of,  48,  49 
Striae,  electrical,  47 
Sunset  disturbances,  64 
Thomson,  J.  J.,  suggestions  of,  25 

Universal  repulsion,  24 

Vapor  of  water,  decomposition  of,  48,  49 
Velocity  of  corpuscles  in  a  conductor, 
41,  45,  46 

Wind-gusts,  magnetic  disturbance  due 

.to,  52,  54,  58,  59 
Wind-mill,  electrical,  2,  5,  7 
Wireless     telegraphing    and    magnetic 

disturbance,  65 
and  the  sunset  effect,  65 

Young,  his  reference  to  solar  outbursts 
and  magnetic  storms,  66 


73 


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